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| author | Carl Byington <carl@five-ten-sg.com> |
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| date | Tue, 18 Sep 2018 09:49:21 -0700 |
| parents | f2bc221240e8 |
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| 108 | 1 <reference> |
| 2 <title>@PACKAGE@ Sendmail milter - Version @VERSION@</title> | |
| 3 <partintro> | |
| 4 <title>Packages</title> | |
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5 |
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6 <para> |
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7 The various source and binary packages are available at <ulink |
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8 url="http://www.five-ten-sg.com/@PACKAGE@/packages/">http://www.five-ten-sg.com/@PACKAGE@/packages/</ulink>. |
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9 The most recent documentation is available at <ulink |
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10 url="http://www.five-ten-sg.com/@PACKAGE@/">http://www.five-ten-sg.com/@PACKAGE@/</ulink>. |
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11 </para> |
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12 |
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13 <para> |
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14 A <ulink |
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15 url="http://www.selenic.com/mercurial/wiki/">Mercurial</ulink> source |
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16 code repository for this project is available at <ulink |
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17 url="http://hg.five-ten-sg.com/@PACKAGE@/">http://hg.five-ten-sg.com/@PACKAGE@/</ulink>. |
| 108 | 18 </para> |
| 94 | 19 |
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20 <para> |
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21 Bitcoin donations for this project may be sent to |
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22 <ulink url="bitcoin:17n5xJZ9a8csJW2uLeZn7i6jegNKGdLUPJ">bitcoin:17n5xJZ9a8csJW2uLeZn7i6jegNKGdLUPJ</ulink> |
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23 </para> |
| 108 | 24 </partintro> |
| 94 | 25 |
| 108 | 26 <refentry id="@PACKAGE@.1"> |
| 27 <refentryinfo> | |
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28 <date>2018-09-18</date> |
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29 <author> |
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30 <firstname>Carl</firstname> |
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31 <surname>Byington</surname> |
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32 <affiliation><orgname>510 Software Group</orgname></affiliation> |
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33 <personblurb><para></para></personblurb> |
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34 </author> |
| 108 | 35 </refentryinfo> |
| 94 | 36 |
| 108 | 37 <refmeta> |
| 38 <refentrytitle>@PACKAGE@</refentrytitle> | |
| 39 <manvolnum>1</manvolnum> | |
| 40 <refmiscinfo>@PACKAGE@ @VERSION@</refmiscinfo> | |
| 41 </refmeta> | |
| 42 | |
| 43 <refnamediv id='name.1'> | |
| 44 <refname>@PACKAGE@</refname> | |
| 45 <refpurpose>a sendmail milter with per-user dnsbl filtering</refpurpose> | |
| 46 </refnamediv> | |
| 94 | 47 |
| 108 | 48 <refsynopsisdiv id='synopsis.1'> |
| 49 <title>Synopsis</title> | |
| 50 <cmdsynopsis> | |
| 51 <command>@PACKAGE@</command> | |
| 52 <arg><option>-c</option></arg> | |
| 53 <arg><option>-s</option></arg> | |
| 54 <arg><option>-d <replaceable class="parameter">n</replaceable></option></arg> | |
| 55 <arg><option>-e <replaceable class="parameter">from|to</replaceable></option></arg> | |
| 179 | 56 <arg><option>-b <replaceable class="parameter">local-domain-socket</replaceable></option></arg> |
| 108 | 57 <arg><option>-r <replaceable class="parameter">local-domain-socket</replaceable></option></arg> |
| 58 <arg><option>-p <replaceable class="parameter">sendmail-socket</replaceable></option></arg> | |
| 59 <arg><option>-t <replaceable class="parameter">timeout</replaceable></option></arg> | |
| 60 </cmdsynopsis> | |
| 61 </refsynopsisdiv> | |
| 94 | 62 |
| 108 | 63 <refsect1 id='options.1'> |
| 64 <title>Options</title> | |
| 65 <variablelist> | |
| 66 <varlistentry> | |
| 67 <term>-c</term> | |
| 111 | 68 <listitem><para> |
| 69 Load the configuration file, print a cannonical form | |
| 70 of the configuration on stdout, and exit. | |
| 71 </para></listitem> | |
| 108 | 72 </varlistentry> |
| 73 <varlistentry> | |
| 74 <term>-s</term> | |
| 111 | 75 <listitem><para> |
| 76 Stress test the configuration loading code by repeating | |
| 77 the load/free cycle in an infinite loop. | |
| 78 </para></listitem> | |
| 108 | 79 </varlistentry> |
| 80 <varlistentry> | |
| 81 <term>-d <replaceable class="parameter">n</replaceable></term> | |
| 111 | 82 <listitem><para> |
| 83 Set the debug level to <replaceable class="parameter">n</replaceable>. | |
| 84 </para></listitem> | |
| 108 | 85 </varlistentry> |
| 86 <varlistentry> | |
| 87 <term>-e <replaceable class="parameter">from|to</replaceable></term> | |
| 111 | 88 <listitem><para> |
| 89 Print the results of looking up the from and to addresses in the | |
| 90 current configuration. The | character is used to separate the from and to | |
| 91 addresses in the argument to the -e switch. | |
| 92 </para></listitem> | |
| 108 | 93 </varlistentry> |
| 94 <varlistentry> | |
| 179 | 95 <term>-b <replaceable class="parameter">local-domain-socket-file-name</replaceable></term> |
| 96 <listitem><para> | |
| 97 Set the local socket used for the connection to the dccifd daemon. | |
| 98 This is typically /var/dcc/dccifd. | |
| 99 </para></listitem> | |
| 100 </varlistentry> | |
| 101 <varlistentry> | |
| 102 <term>-r <replaceable class="parameter">local-domain-socket-file-name</replaceable></term> | |
| 111 | 103 <listitem><para> |
| 104 Set the local socket used for the connection to our own dns resolver processes. | |
| 105 </para></listitem> | |
| 108 | 106 </varlistentry> |
| 107 <varlistentry> | |
| 108 <term>-p <replaceable class="parameter">sendmail-socket</replaceable></term> | |
| 111 | 109 <listitem><para> |
| 110 Set the socket used for the milter connection to sendmail. This is either | |
| 111 "inet:port@ip-address" or "local:local-domain-socket-file-name". | |
| 112 </para></listitem> | |
| 108 | 113 </varlistentry> |
| 114 <varlistentry> | |
| 115 <term>-t <replaceable class="parameter">timeout</replaceable></term> | |
| 111 | 116 <listitem><para> |
| 117 Set the timeout in seconds used for communication with sendmail. | |
| 118 </para></listitem> | |
| 108 | 119 </varlistentry> |
| 120 </variablelist> | |
| 121 </refsect1> | |
| 94 | 122 |
| 111 | 123 <refsect1 id='usage.1'> |
| 108 | 124 <title>Usage</title> |
| 125 <para><command>@PACKAGE@</command> -c</para> | |
| 126 <para><command>@PACKAGE@</command> -s</para> | |
| 111 | 127 <para><command>@PACKAGE@</command> -e 'someone@aol.com|localname@mydomain.tld'</para> |
| 128 <para><command>@PACKAGE@</command> -d 10 -r resolver.sock -p local:dnsbl.sock</para> | |
| 129 </refsect1> | |
| 130 | |
| 131 <refsect1 id='installation.1'> | |
| 132 <title>Installation</title> | |
| 133 <para> | |
| 134 This is now a standard GNU autoconf/automake installation, so the normal | |
| 135 "./configure; make; su; make install" works. "make chkconfig" will | |
| 136 setup the init.d runlevel scripts. Alternatively, you can use the | |
| 137 source or binary RPMs at <ulink | |
| 138 url="http://www.five-ten-sg.com/@PACKAGE@/packages">http://www.five-ten-sg.com/@PACKAGE@/packages</ulink>. | |
| 139 </para> | |
| 140 <para> | |
| 141 Note that this has ONLY been tested on Linux, specifically RedHat Linux. | |
| 142 In particular, this milter makes no attempt to understand IPv6. Your | |
| 143 mileage will vary. You will need at a minimum a C++ compiler with a | |
| 144 minimally thread safe STL implementation. The distribution includes a | |
| 145 test.cpp program. If it fails this milter won't work. If it passes, | |
| 146 this milter might work. | |
| 147 </para> | |
| 148 <para> | |
| 149 Modify your sendmail.mc by removing all the "FEATURE(dnsbl" lines, add | |
| 150 the following line in your sendmail.mc and rebuild the .cf file | |
| 151 </para> | |
| 152 <para><screen>INPUT_MAIL_FILTER(`dnsbl', `S=local:/var/run/dnsbl/dnsbl.sock, F=T, T=C:30s;S:5m;R:5m;E:5m')</screen></para> | |
| 153 <para> | |
| 154 Modify the default <citerefentry> | |
| 155 <refentrytitle>@PACKAGE@.conf</refentrytitle> <manvolnum>5</manvolnum> | |
| 156 </citerefentry> configuration. | |
| 157 </para> | |
| 158 </refsect1> | |
| 159 | |
| 160 <refsect1 id='configuration.1'> | |
| 161 <title>Configuration</title> | |
| 162 <para> | |
| 163 The configuration file is documented in <citerefentry> | |
| 164 <refentrytitle>@PACKAGE@.conf</refentrytitle> <manvolnum>5</manvolnum> | |
| 165 </citerefentry>. Any change to the config file, or any file included | |
| 166 from that config file, will cause it to be reloaded within three | |
| 167 minutes. | |
| 168 </para> | |
| 108 | 169 </refsect1> |
| 94 | 170 |
| 108 | 171 <refsect1 id='introduction.1'> |
| 172 <title>Introduction</title> | |
| 173 <para> | |
| 174 Consider the case of a mail server that is acting as secondary MX for a | |
| 175 collection of clients, each of which has a collection of mail domains. | |
| 176 Each client may use their own collection of DNSBLs on their primary mail | |
| 177 server. We present here a mechanism whereby the backup mail server can | |
| 178 use the correct set of DNSBLs for each recipient for each message. As a | |
| 179 side-effect, it gives us the ability to customize the set of DNSBLs on a | |
| 183 | 180 per-recipient basis, so that fred@example.com could use LOCAL and the |
| 108 | 181 SBL, where all other users @example.com use only the SBL. |
| 182 </para> | |
| 183 <para> | |
| 184 This milter can also verify the envelope from/recipient pairs with the | |
| 185 primary MX server. This allows the backup mail servers to properly | |
| 186 reject mail sent to invalid addresses. Otherwise, the backup mail | |
| 187 servers will accept that mail, and then generate a bounce message when | |
| 188 the message is forwarded to the primary server (and rejected there with | |
| 127 | 189 no such user). These rejections are the primary cause of such backscatter. |
| 108 | 190 </para> |
| 191 <para> | |
| 192 This milter will also decode (uuencode, base64, mime, html entity, url | |
| 193 encodings) and scan for HTTP and HTTPS URLs and bare hostnames in the | |
| 194 body of the mail. If any of those host names have A or NS records on | |
| 195 the SBL (or a single configurable DNSBL), the mail will be rejected | |
| 196 unless previously whitelisted. This milter also counts the number of | |
| 197 invalid HTML tags, and can reject mail if that count exceeds your | |
| 198 specified limit. | |
| 199 </para> | |
| 200 <para> | |
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201 This milter can also impose hourly and daily rate |
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202 limits on the number of recipients accepted from SMTP |
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203 AUTH connections, that would otherwise be allowed to |
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204 relay thru this mail server with no spam filtering. If |
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205 the connection does not use SMTP AUTH, the rate limits |
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206 may be specified by the mail from email address or |
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207 domain. |
| 136 | 208 </para> |
| 209 <para> | |
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210 This milter can also impose hourly and daily limits on the number of |
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211 different ip addresses used for SMTP AUTH connections. If a single |
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212 user is connecting from too many different ip addresses, we presume that |
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213 their authentication credentials have been discovered, and block their |
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214 outgoing mail. |
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215 </para> |
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216 <para> |
| 162 | 217 Consider the case of a message from A to B passing thru this milter. If |
| 218 that message is not blocked, then we might eventually see a reply | |
| 156 | 219 message from B to A. If the filtering context for A includes an |
| 162 | 220 autowhite entry, and that context does <emphasis>not</emphasis> cover B |
| 221 as a recipient, then this milter will add an entry in that file to | |
| 222 whitelist such replies for a configurable time period. Suppose A and B | |
| 223 are in the same domain, or at least use the same filtering context. In | |
| 224 that case we don't want to add a whitelist entry for B, since that would | |
| 225 then allow spammers to send mail from B (forged) to B. Such autowhite | |
| 160 | 226 files need to be writeable by the dnsbl user, where all the other dnsbl |
| 227 configuration files only need to be readable by the dnsbl user. | |
| 156 | 228 </para> |
| 229 <para> | |
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230 You can manually add such an autowhite entry, by appending a single |
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231 text line to the autowhitelist file, using something like |
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232 <command>echo "$mail 0" >>$autowhitefile</command>. |
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233 You can manually remove such an autowhite entry, by appending a single |
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234 text line to the autowhitelist file, using something like |
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235 <command>echo "$mail 1" >>$autowhitefile</command>. |
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236 </para> |
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237 <para> |
| 108 | 238 The DNSBL milter reads a text configuration file (dnsbl.conf) on |
| 239 startup, and whenever the config file (or any of the referenced include | |
| 240 files) is changed. The entire configuration file is case insensitive. | |
| 241 If the configuration cannot be loaded due to a syntax error, the milter | |
| 242 will log the error and quit. If the configuration cannot be reloaded | |
| 243 after being modified, the milter will log the error and send an email to | |
| 152 | 244 root from dnsbl@$hostname. You probably want to add dnsbl@$hostname |
| 108 | 245 to your /etc/mail/virtusertable since otherwise sendmail will reject |
| 246 that message. | |
| 247 </para> | |
| 248 </refsect1> | |
| 94 | 249 |
| 111 | 250 <refsect1 id='dcc.1'> |
| 108 | 251 <title>DCC Issues</title> |
| 252 <para> | |
| 253 If you are also using the <ulink | |
| 254 url="http://www.rhyolite.com/anti-spam/dcc/">DCC</ulink> milter, there | |
| 255 are a few considerations. You may need to whitelist senders from the | |
| 256 DCC bulk detector, or from the DNS based lists. Those are two very | |
| 257 different reasons for whitelisting. The former is done thru the DCC | |
| 258 whiteclnt config file, the later is done thru the DNSBL milter config | |
| 259 file. | |
| 260 </para> | |
| 261 <para> | |
| 262 You may want to blacklist some specific senders or sending domains. | |
| 263 This could be done thru either the DCC (on a global basis, or for a | |
| 264 specific single recipient). We prefer to do such blacklisting via the | |
| 265 DNSBL milter config, since it can be done for a collection of recipient | |
| 266 mail domains. The DCC approach has the feature that you can capture the | |
| 267 entire message in the DCC log files. The DNSBL milter approach has the | |
| 268 feature that the mail is rejected earlier (at RCPT TO time), and the | |
| 269 sending machine just gets a generic "550 5.7.1 no such user" message. | |
| 270 </para> | |
| 271 <para> | |
| 272 The DCC whiteclnt file can be included in the DNSBL milter config by the | |
| 273 dcc_to and dcc_from statements. This will import the (env_to, env_from, | |
| 274 and substitute mail_host) entries from the DCC config into the DNSBL | |
| 275 config. This allows using the DCC config as the single point for | |
| 276 white/blacklisting. | |
| 277 </para> | |
| 278 <para> | |
| 279 Consider the case where you have multiple clients, each with their own | |
| 280 mail servers, and each running their own DCC milters. Each client is | |
| 281 using the DCC facilities for envelope from/to white/blacklisting. | |
| 282 Presumably you can use rsync or scp to fetch copies of your clients DCC | |
| 283 whiteclnt files on a regular basis. Your mail server, acting as a | |
| 284 backup MX for your clients, can use the DNSBL milter, and include those | |
| 285 client DCC config files. The envelope from/to white/blacklisting will | |
| 286 be appropriately tagged and used only for the domains controlled by each | |
| 287 of those clients. | |
| 288 </para> | |
| 179 | 289 <para> |
| 290 You can now use (via dccifd) different dcc filtering parameters on a per | |
| 291 context basis. See the dcc_greylist and dcc_bulk_threshold statements | |
| 292 in the <citerefentry> <refentrytitle>@PACKAGE@.conf</refentrytitle> | |
| 293 <manvolnum>5</manvolnum> </citerefentry> configuration. Those | |
| 294 statements are only active if you supply the <option>-b</option> option | |
| 295 on the dnsbl command line. If you use the dcc via the standard dcc | |
| 296 milter (dccm), then connections from clients that use SMTP AUTH are | |
| 297 still subject to greylisting. If you use the dcc via dccifd and this | |
| 298 milter, then connections from clients that use SMTP AUTH are never | |
| 180 | 299 subject to greylisting. As part of this per-user greylisting, you need |
| 300 to move the dnsblnogrey file from the config directory to something | |
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301 like /var/dcc/userdirs/dnsblnogrey/whiteclnt so the dccifd will |
| 180 | 302 properly ignore greylisting for those recipients that don't want it. |
| 179 | 303 </para> |
| 108 | 304 </refsect1> |
| 94 | 305 |
| 111 | 306 <refsect1 id='definitions.1'> |
| 108 | 307 <title>Definitions</title> |
| 308 <para> | |
| 309 CONTEXT - a collection of parameters that defines the filtering context | |
| 310 to be used for a collection of envelope recipient addresses. The | |
| 311 context includes such things as the list of DNSBLs to be used, and the | |
| 312 various content filtering parameters. | |
| 313 </para> | |
| 314 <para> | |
| 315 DNSBL - a named DNS based blocking list is defined by a dns suffix (e.g. | |
| 316 sbl-xbl.spamhaus.org) and a message string that is used to generate the | |
| 317 "550 5.7.1" smtp error return code. The names of these DNSBLs will be | |
| 318 used to define the DNSBL-LISTs. | |
| 319 </para> | |
| 320 <para> | |
| 321 DNSBL-LIST - a named list of DNSBLs that will be used for specific | |
| 322 recipients or recipient domains. | |
| 323 </para> | |
| 249 | 324 <para> |
| 325 DNSWL - a named DNS based white list is defined by a dns suffix (e.g. | |
| 326 list.dnswl.org) and an integer level. If the level is greater than or | |
| 327 equal to x in the 127.0.z.x return code from the white list, then the | |
| 328 ip address is considered to match, and the message will be whitelisted. | |
| 329 The names of these DNSWLs will be used to define the DNSWL-LISTs. | |
| 330 </para> | |
| 331 <para> | |
| 332 DNSWL-LIST - a named list of DNSWLs that will be used for specific | |
| 333 recipients or recipient domains. | |
| 334 </para> | |
| 108 | 335 </refsect1> |
| 94 | 336 |
| 111 | 337 <refsect1 id='filtering.1'> |
| 108 | 338 <title>Filtering Procedure</title> |
| 339 <para> | |
| 152 | 340 The SMTP envelope 'from' and 'to' values are used in various checks. |
| 341 The first check is to see if a reply message (swapping the env_from and | |
| 160 | 342 env_to values) would be unconditionally blocked (just based on the |
| 343 envelope from address). That check is similar to the main check | |
| 344 described below, but there is no body content to be scanned, and there | |
| 345 is no client connection ip address to be checked against DNSBLs. If | |
| 346 such a reply message would be blocked, we also block the original | |
| 347 outgoing message. This prevents folks from sending mail to recipients | |
| 348 that are unable to reply. | |
| 152 | 349 </para> |
| 350 <para> | |
|
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351 If the client has authenticated with sendmail, the recipient rate limits |
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352 and connection ip address limits are |
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353 checked. If the authenticated user has not exceeded the hourly or daily rate |
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354 limits, then the mail is accepted, the filtering contexts are not used, |
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355 the dns lists are not checked, and the body content is not scanned. These |
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356 rate limits can also be applied to unauthenticated connections, in which case |
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357 the envelope from value is used as the authentication id for lookup purposes. |
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358 If |
| 136 | 359 the client has not authenticated with sendmail, we follow these steps |
| 360 for each recipient. | |
| 108 | 361 </para> |
| 362 <orderedlist> | |
| 111 | 363 <listitem><para> |
| 108 | 364 The envelope to email address is used to find an initial filtering |
| 365 context. We first look for a context that specified the full email | |
| 366 address in the env_to statement. If that is not found, we look for a | |
| 367 context that specified the entire domain name of the envelope recipient | |
| 368 in the env_to statement. If that is not found, we look for a context | |
| 369 that specified the user@ part of the envelope recipient in the env_to | |
| 370 statement. If that is not found, we use the first top level context | |
| 371 defined in the config file. | |
| 111 | 372 </para></listitem> |
| 373 <listitem><para> | |
| 108 | 374 The initial filtering context may redirect to a child context based on |
| 375 the values in the initial context's env_from statement. We look for [1) | |
| 376 the full envelope from email address, 2) the domain name part of the | |
| 377 envelope from address, 3) the user@ part of the envelope from address] | |
| 378 in that context's env_from statement, with values that point to a child | |
| 379 context. If such an entry is found, we switch to that child filtering | |
| 380 context. | |
| 111 | 381 </para></listitem> |
| 382 <listitem><para> | |
| 108 | 383 We lookup [1) the full envelope from email address, 2) the domain name |
| 384 part of the envelope from address, 3) the user@ part of the envelope | |
| 385 from address] in the filtering context env_from statement. That results | |
| 386 in one of (white, black, unknown, inherit). | |
| 111 | 387 </para></listitem> |
| 388 <listitem><para> | |
| 108 | 389 If the answer is black, mail to this recipient is rejected with "no such |
| 390 user", and the dns lists are not checked. | |
| 111 | 391 </para></listitem> |
| 392 <listitem><para> | |
|
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393 If the answer is white, the mail is not from localhost, |
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394 and the envelope from domain name is listed in the current (or parents) |
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395 filtering contexts dkim_from with "required_signed" or "unsigned_black", |
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396 we downgrade this white answer to unknown. If the answer is still white, |
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397 mail to this recipient is accepted and the dns lists are not checked. |
| 111 | 398 </para></listitem> |
| 399 <listitem><para> | |
| 108 | 400 If the answer is unknown, we don't reject yet, but the dns lists will be |
| 401 checked, and the content may be scanned. | |
| 111 | 402 </para></listitem> |
| 403 <listitem><para> | |
| 108 | 404 If the answer is inherit, we repeat the envelope from search in the |
| 405 parent context. | |
| 111 | 406 </para></listitem> |
| 407 <listitem><para> | |
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408 If the mail has not been accepted or rejected yet, and the filtering |
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409 context (or any ancestor context) specifies a non-empty whitelist regular |
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410 expression, then we check the envelope from value against that regex. |
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411 The mail is accepted if the envelope from value matches the specified regular |
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412 expression. |
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413 </para></listitem> |
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414 <listitem><para> |
|
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415 If the mail has not been accepted or rejected yet, and the envelope from |
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416 email address is not empty, the dns white lists |
| 249 | 417 specified in the filtering context are checked and the mail is accepted |
| 418 if any list has an A record for the standard dns based lookup scheme | |
| 419 (reversed octets of the client followed by the dns suffix) with a final | |
| 420 octet greater than or equal to the level specified for that dnswl. | |
| 421 </para></listitem> | |
| 422 <listitem><para> | |
| 423 If the mail has not been accepted or rejected yet, the dns black lists | |
| 168 | 424 specified in the filtering context are checked and the mail is rejected |
| 425 if any list has an A record for the standard dns based lookup scheme | |
| 426 (reversed octets of the client followed by the dns suffix). | |
| 427 </para></listitem> | |
| 428 <listitem><para> | |
| 429 If the mail has not been accepted or rejected yet, and the filtering | |
|
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430 context (or any ancestor context) requires matching reverse dns client |
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431 name, the mail is rejected if the client name is empty or forged. |
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432 </para></listitem> |
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433 <listitem><para> |
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434 If the mail has not been accepted or rejected yet, and the filtering |
| 170 | 435 context (or any ancestor context) specifies a non-empty generic regular |
| 436 expression, then we check the fully qualified client name (obtained via | |
| 437 the sendmail macro "_"). The mail is rejected if the client name | |
| 438 matches the specified regular expression. | |
| 111 | 439 </para></listitem> |
| 440 <listitem><para> | |
| 108 | 441 If the mail has not been accepted or rejected yet, we look for a |
| 442 verification context, which is the closest ancestor of the filtering | |
| 443 context that both specifies a verification host, and which covers the | |
| 444 envelope to address. If we find such a verification context, and the | |
| 445 verification host is not our own hostname, we open an smtp conversation | |
| 446 with that verification host. The current envelope from and recipient to | |
| 447 values are passed to that verification host. If we receive a 5xy | |
| 448 response those commands, we reject the current recipient with "no such | |
| 449 user". | |
| 111 | 450 </para></listitem> |
| 451 <listitem><para> | |
| 108 | 452 If the mail has not been accepted or rejected yet, and the filtering |
| 453 context enables content filtering, and this is the first such recipient | |
| 454 in this smtp transaction, we set the content filtering parameters from | |
| 455 this context, and enable content filtering for the body of this message. | |
| 111 | 456 </para></listitem> |
| 108 | 457 </orderedlist> |
| 458 <para> | |
| 160 | 459 For each recipient that was accepted, we search for an autowhite entry |
| 460 starting in the reply filtering context. If an autowhite entry is found, | |
|
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461 and the local part of the recipient address is shorter than 35 characters, |
| 160 | 462 we add the recipient to that auto whitelist file. This will prevent reply |
| 463 messages from being blocked by the dnsbl or content filtering. | |
| 464 </para> | |
| 465 <para> | |
|
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466 If the mail is from localhost we skip the following dkim checks, since |
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467 such mail will never be dkim signed. This is typically mail that is generated by |
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468 apache forms. |
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469 </para> |
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470 <para> |
|
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471 If content filtering is enabled for this body, we look for dkim_signer |
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472 and dkim_from sections in the current context and parents. We collect the |
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473 signers of this message from the header added by the dkim-milter. If any |
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474 of the message signers are whitelisted, the message is accepted. |
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475 </para> |
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476 <para> |
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477 If the header from domain maps to required_signed then: |
|
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478 If any of the message signers are in that list, or if |
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479 the source ip address passes a strong spf check for the header from |
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480 domain, the message is accepted. Otherwise, the message is rejected. |
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481 </para> |
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482 <para> |
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483 If the header from domain maps to signed_white then: |
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484 If any of the message signers are in that list, or if |
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485 the source ip address passes a strong spf check for the header from |
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486 domain, the message is accepted. Otherwise, processing continues. |
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487 </para> |
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488 <para> |
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489 If the header from domain maps to signed_black then: |
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490 If any of the message signers are in that list, the message is rejected. |
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491 Otherwise, processing continues. |
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492 </para> |
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493 <para> |
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494 If the header from domain maps to unsigned_black then: |
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495 If any of the message signers are in that list, or if |
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496 the source ip address passes a strong spf check for the header from |
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497 domain, processing continues. Otherwise, the message is rejected. |
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498 This is very close to enforcing DMARC for the header from domain. |
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499 </para> |
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500 <para> |
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501 If any of the message signers are blacklisted, the message is rejected. |
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502 </para> |
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503 <para> |
| 108 | 504 If content filtering is enabled for this body, the mail text is decoded |
| 119 | 505 (uuencode, base64, mime, html entity, url encodings), and scanned for HTTP |
| 506 and HTTPS URLs or bare host names. Hostnames must be either ip address | |
| 507 literals, or must end in a string defined by the TLD list. The first | |
| 508 <configurable> host names are checked as follows. | |
| 509 </para> | |
| 510 <para> | |
| 511 The only known list that is suitable for the content filter DNSBL is the | |
| 512 SBL. If the content filter DNSBL is defined, and any of those host | |
| 513 names resolve to ip addresses that are on that DNSBL (or have | |
| 514 nameservers that are on that list), and the host name is not on the | |
| 515 <configurable> ignore list, the mail is rejected. | |
| 516 </para> | |
| 517 <para> | |
| 518 If the content uribl DNSBL is defined, and any of those host names are | |
| 519 on that DNSBL, and the host name is not on the <configurable> | |
|
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520 ignore list, the mail is rejected. There are three lists that are suitable |
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521 here, URIBL, SURBL, and DBL. |
| 119 | 522 </para> |
| 523 <para> | |
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524 If any non-whitelisted recipient has a filtering context with a non-zero |
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525 spamassassin limit, then the message is passed thru spamassassin (via |
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526 spamc), and the message is rejected for those recipients with spamassassin |
|
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527 limits less than the resulting spamassassin score. For example, a |
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528 spamassassin limit of three will reject messages with spamassassin scores |
|
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529 of four or greater. If the filtering context has a spamassassin limit of |
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530 zero, then spamassassin is not called (or if called the results are not used) |
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531 for this recipient. |
|
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532 </para> |
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533 <para> |
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534 If any non-whitelisted recipient has a filtering context that specifies |
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535 DCC greylisting, then the message is passed thru the DCC bulk detector, |
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536 and the message is greylisted (for all recipients) if the DCC says this |
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537 message should be delayed. |
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538 </para> |
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539 <para> |
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540 If any non-whitelisted recipient has a filtering context with a non-zero |
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541 DCC bulk threshold, then the message is passed thru the DCC bulk detector, |
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542 and the message is rejected for those recipients with DCC thresholds less |
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543 than or equal to the DCC bulk score. |
| 163 | 544 </para> |
| 545 <para> | |
| 119 | 546 We also scan for excessive bad html tags, and if a <configurable> |
| 547 limit is exceeded, the mail is rejected. | |
| 108 | 548 </para> |
| 549 </refsect1> | |
| 94 | 550 |
|
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551 <refsect1 id='dmarc.1'> |
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552 <title>DMARC vs dkim_from require_signed</title> |
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553 <para> |
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554 Note that DNSBL does not implement rfc7489 DMARC. We do not look for |
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555 _dmarc.$DOMAIN txt records. |
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556 </para> |
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557 <para> |
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558 The restrictions imposed by require_signed are similar but not |
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559 identical to a DMARC reject policy with strict identifier alignment. |
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560 When doing SPF fallback, DMARC checks SPF based on the rfc5321 |
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561 envelope from domain. DNSBL checks SPF based on the rfc5322 header |
|
426
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562 from domain. |
|
409
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563 DMARC does not allow mail from good.example.com to be |
|
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564 signed by trusted.example.net - which is a common case. Both Microsoft |
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565 Office365 and Google run mail for customer domains, but use DKIM |
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566 signing domains in onmicrosoft.com and gappssmtp.com, which are |
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567 unrelated to the customer domain. DMARC in the default relaxed |
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568 alignment mode allows evil.example.com to sign mail from |
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569 good.example.com. DNSBL specifies the exact list of acceptable signing |
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570 domains, rather than inferring it from child/parent relationships, or |
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571 using public |
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572 suffix lists to find the organizational domain. We can block mail |
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573 from marketing.example.com while accepting mail from |
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574 billing.example.com, even if both are DKIM signed by example.com. |
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575 </para> |
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576 <para> |
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577 Suppose we have: |
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578 <literallayout class="monospaced"><![CDATA[ |
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579 rfc5321 envelope from = one@evil.example.com |
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580 rfc5322 header from = two@good.example.com |
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581 authentication results = dkim pass header.d=other.example.com |
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582 _dmarc.good.example.com txt = "v=DMARC1; p=reject; adkim:s aspf:s" |
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583 dkim_from {good.example.com require_signed other.example.com;} |
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584 ]]></literallayout> |
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585 DMARC would fail the strict identifier alignment. DNSBL allows |
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586 us to require DKIM signatures that are unrelated |
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587 to the rfc5322 header from, so we accept this message. |
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588 </para> |
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589 <para> |
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590 Suppose we have: |
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591 <literallayout class="monospaced"><![CDATA[ |
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592 rfc5321 envelope from = one@evil.example.com |
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593 rfc5322 header from = two@good.example.com |
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594 authentication results = dkim pass header.d=other.example.net |
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595 _dmarc.good.example.com txt = "v=DMARC1; p=reject; adkim:r aspf:r" |
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596 dkim_from {good.example.com require_signed other.example.net;} |
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597 ]]></literallayout> |
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598 DMARC would pass the relaxed spf identifier alignments, |
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599 and would check the evil.example.com spf record. If that |
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600 allowed the source ip, DMARC would accept the message. |
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601 DMARC would not check DKIM since example.com and example.net |
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602 do not pass even the relaxed identifer alignment requirement. |
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603 DNSBL allows us to require DKIM signatures that are not |
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604 related to the rfc5322 header from domain, so we accept |
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605 the message based on the DKIM signature and don't need to |
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606 fall back to SPF. |
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607 </para> |
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608 <para> |
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609 Suppose we have: |
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610 <literallayout class="monospaced"><![CDATA[ |
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611 rfc5321 envelope from = one@evil.example.com |
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612 rfc5322 header from = two@good.example.com |
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613 authentication results = dkim fail header.d=other.example.net |
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614 _dmarc.good.example.com txt = "v=DMARC1; p=reject; adkim:r aspf:r" |
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615 evil.example.com txt = "v=spf1 ... including the source ip |
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616 good.example.com txt = "v=spf1 ... not including the source ip |
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617 dkim_from {good.example.com require_signed other.example.net;} |
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618 ]]></literallayout> |
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619 DNSBL allows us to require DKIM signatures that are not |
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620 related to the rfc5322 header from domain. In this case |
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621 the signature fails, so we fall back to an SPF check. |
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622 We check SPF based on the rfc5322 header from, and |
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623 good.example.com does not allow the source ip, so we reject |
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624 this message. |
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625 DMARC would accept that message based on the SPF check |
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626 for evil.example.com |
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627 </para> |
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628 </refsect1> |
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629 |
| 111 | 630 <refsect1 id='access.1'> |
| 108 | 631 <title>Sendmail access vs. DNSBL</title> |
| 632 <para> | |
| 633 With the standard sendmail.mc dnsbl FEATURE, the dnsbl checks may be | |
| 634 suppressed by entries in the /etc/mail/access database. For example, | |
| 635 suppose you control a /18 of address space, and have allocated some /24s | |
| 636 to some clients. You have access entries like | |
| 111 | 637 <literallayout class="monospaced"><![CDATA[ |
| 638 192.168.4 OK | |
| 639 192.168.17 OK]]></literallayout> | |
| 108 | 640 </para> |
| 641 <para> | |
| 642 to allow those clients to smarthost thru your mail server. Now if one | |
| 643 of those clients happens get infected with a virus that turns a machine | |
| 644 into an open proxy, and their 192.168.4.45 lands on the SBL-XBL, you | |
| 645 will still wind up allowing that infected machine to smarthost thru your | |
| 646 mail servers. | |
| 647 </para> | |
| 648 <para> | |
| 649 With this DNSBL milter, the sendmail access database cannot override the | |
| 650 dnsbl checks, so that machine won't be able to send mail to or thru your | |
| 651 smarthost mail server (unless the virus/proxy can use smtp-auth). | |
| 652 </para> | |
| 653 <para> | |
| 654 Using the standard sendmail features, you would add access entries to | |
| 655 allow hosts on your local network to relay thru your mail server. Those | |
| 656 OK entries in the sendmail access database will override all the dnsbl | |
| 657 checks. With this DNSBL milter, you will need to have the local users | |
| 658 authenticate with smtp-auth to get the same effect. You might find | |
| 659 <ulink | |
| 660 url="http://www.ists.dartmouth.edu/classroom/sendmail-ssl-how-to.php"> | |
| 661 these directions</ulink> helpful for setting up smtp-auth if you are on | |
| 662 RH Linux. | |
| 663 </para> | |
| 664 </refsect1> | |
| 94 | 665 |
| 111 | 666 <refsect1 id='performance.1'> |
| 108 | 667 <title>Performance Issues</title> |
| 668 <para> | |
| 669 Consider a high volume high performance machine running sendmail. Each | |
| 670 sendmail process can do its own dns resolution. Typically, such dns | |
| 671 resolver libraries are not thread safe, and so must be protected by some | |
| 672 sort of mutex in a threaded environment. When we add a milter to | |
| 673 sendmail, we now have a collection of sendmail processes, and a | |
| 674 collection of milter threads. | |
| 675 </para> | |
| 676 <para> | |
| 677 We will be doing a lot of dns lookups per mail message, and at least | |
| 678 some of those will take many tens of seconds. If all this dns work is | |
| 679 serialized inside the milter, we have an upper limit of about 25K mail | |
| 680 messages per day. That is clearly not sufficient for many sites. | |
| 681 </para> | |
| 682 <para> | |
| 683 Since we want to do parallel dns resolution across those milter threads, | |
| 684 we add another collection of dns resolver processes. Each sendmail | |
| 685 process is talking to a milter thread over a socket, and each milter | |
| 686 thread is talking to a dns resolver process over another socket. | |
| 687 </para> | |
| 688 <para> | |
| 689 Suppose we are processing 20 messages per second, and each message | |
| 690 requires 20 seconds of dns work. Then we will have 400 sendmail | |
| 691 processes, 400 milter threads, and 400 dns resolver processes. Of | |
| 692 course that steady state is very unlikely to happen. | |
| 693 </para> | |
| 694 </refsect1> | |
| 94 | 695 |
| 696 | |
| 111 | 697 <refsect1 id='rejected.1'> |
| 108 | 698 <title>Rejected Ideas</title> |
| 699 <para> | |
| 700 The following ideas have been considered and rejected. | |
| 701 </para> | |
| 702 <para> | |
| 111 | 703 Add max_recipients setting to the context configuration. Recipients in |
| 704 excess of that limit will be rejected, and all the non-whitelisted | |
| 705 recipients will be removed. Current spammers *very* rarely send more | |
| 706 than ten recipients in a single smtp transaction, so this won't stop any | |
| 108 | 707 significant amount of spam. |
| 708 </para> | |
| 709 <para> | |
| 710 Add poison addresses to the configuration. If any recipient is | |
| 711 poison, all recipients are rejected even if they would be whitelisted, | |
| 712 and the data is rejected if sent. I have a collection of spam trap | |
| 713 addresses that would be suitable for such use. Based on my log files, | |
| 714 any mail to those spam trap addresses is rejected based on either dnsbl | |
| 715 lookups or the DCC. So this won't result in blocking any additional | |
| 716 spam. | |
| 717 </para> | |
| 718 <para> | |
| 719 Add an option to only allow one recipient if the return path is | |
| 720 empty. Based on my log files, there is no mail that violates this | |
| 721 check. | |
| 722 </para> | |
| 723 <para> | |
| 724 Reject the mail if the envelope from domain name contains any MX | |
| 725 records pointing to 127.0.0.0/8. I don't see any significant amount of | |
| 726 spam sent with such domain names. | |
| 727 </para> | |
| 728 </refsect1> | |
| 94 | 729 |
| 108 | 730 <refsect1 id='todo.1'> |
| 731 <title>TODO</title> | |
| 732 <para> | |
| 733 The following ideas are under consideration. | |
| 734 </para> | |
| 735 <para> | |
|
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736 More complete SPF check. |
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737 </para> |
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738 <para> |
| 276 | 739 Add config switch to require the HELO argument to resolve to an ip address. |
| 740 </para> | |
| 741 <para> | |
|
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742 Add white/unknown to config for smtp authenticated connections. Currently |
|
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743 any authenticated connection is fully whitelisted. The only spam control |
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744 on those connections is rate limiting. This feature would allow content based |
|
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745 spam controls to be applied even to authenticated connections. Add |
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746 context/authenticated_dnsbl_list and context/content/authenticated. |
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747 </para> |
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748 <para> |
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749 Add an optional list of domains to be enforced on the env_from value for |
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750 authenticated connections. User abc could be restricted to envelope from |
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751 values of a.com and b.com, user def could be restricted to envelope from |
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752 values of dd.com and ee.com. |
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753 </para> |
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754 <para> |
| 115 | 755 Look for href="hostname/path" strings that are missing the required |
| 756 http:// protocol header. Such references are still clickable in common | |
| 757 mail software. | |
| 758 </para> | |
| 108 | 759 </refsect1> |
| 94 | 760 |
| 111 | 761 <refsect1 id='copyright.1'> |
| 108 | 762 <title>Copyright</title> |
| 763 <para> | |
|
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764 Copyright (C) 2012 by 510 Software Group <carl@five-ten-sg.com> |
| 108 | 765 </para> |
| 766 <para> | |
| 767 This program is free software; you can redistribute it and/or modify it | |
| 768 under the terms of the GNU General Public License as published by the | |
| 160 | 769 Free Software Foundation; either version 3, or (at your option) any |
| 108 | 770 later version. |
| 771 </para> | |
| 772 <para> | |
| 773 You should have received a copy of the GNU General Public License along | |
| 774 with this program; see the file COPYING. If not, please write to the | |
| 775 Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. | |
| 776 </para> | |
| 777 </refsect1> | |
| 94 | 778 |
| 111 | 779 <refsect1 id='version.1'> |
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780 <title>Version</title> |
| 108 | 781 <para> |
|
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782 @VERSION@ |
| 108 | 783 </para> |
| 784 </refsect1> | |
| 785 </refentry> | |
| 786 | |
| 787 | |
| 788 <refentry id="@PACKAGE@.conf.5"> | |
| 789 <refentryinfo> | |
|
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790 <date>2018-09-18</date> |
|
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791 <author> |
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792 <firstname>Carl</firstname> |
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793 <surname>Byington</surname> |
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794 <affiliation><orgname>510 Software Group</orgname></affiliation> |
|
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795 <personblurb><para></para></personblurb> |
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796 </author> |
| 108 | 797 </refentryinfo> |
| 94 | 798 |
| 108 | 799 <refmeta> |
| 800 <refentrytitle>@PACKAGE@.conf</refentrytitle> | |
| 801 <manvolnum>5</manvolnum> | |
| 802 <refmiscinfo>@PACKAGE@ @VERSION@</refmiscinfo> | |
| 803 </refmeta> | |
| 94 | 804 |
| 108 | 805 <refnamediv id='name.5'> |
| 806 <refname>@PACKAGE@.conf</refname> | |
| 111 | 807 <refpurpose>configuration file for @PACKAGE@ sendmail milter</refpurpose> |
| 108 | 808 </refnamediv> |
| 809 | |
| 810 <refsynopsisdiv id='synopsis.5'> | |
| 811 <title>Synopsis</title> | |
| 812 <cmdsynopsis> | |
| 813 <command>@PACKAGE@.conf</command> | |
| 814 </cmdsynopsis> | |
| 815 </refsynopsisdiv> | |
| 94 | 816 |
| 108 | 817 <refsect1 id='description.5'> |
| 818 <title>Description</title> | |
| 819 <para>The <command>@PACKAGE@.conf</command> configuration file is | |
|
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820 specified by this partial bnf description. Comments start with // |
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821 or # and extend to the end of the line. To include the contents |
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823 <literallayout class="monospaced"><![CDATA[include "<file>";]]></literallayout> |
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824 </para> |
| 108 | 825 |
| 826 <literallayout class="monospaced"><![CDATA[ | |
| 827 CONFIG = {CONTEXT ";"}+ | |
| 828 CONTEXT = "context" NAME "{" {STATEMENT}+ "}" | |
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829 STATEMENT = ( DNSBL | DNSBLLIST | DNSWL | DNSWLLIST | CONTENT | ENV-TO |
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830 | VERIFY | GENERIC | W_REGEX | AUTOWHITE | CONTEXT | ENV-FROM |
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831 | RATE-LIMIT | REQUIRERDNS) ";" |
| 108 | 832 |
| 124 | 833 DNSBL = "dnsbl" NAME DNSPREFIX ERROR-MSG1 |
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834 DNSBLLIST = "dnsbl_list" {NAME}* |
| 108 | 835 |
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836 DNSWL = "dnswl" NAME DNSPREFIX LEVEL |
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837 DNSWLLIST = "dnswl_list" {NAME}* |
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838 LEVEL = INTEGER |
| 94 | 839 |
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840 REQUIRERDNS = "require_rdns" ("yes" | "no") |
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841 |
| 108 | 842 CONTENT = "content" ("on" | "off") "{" {CONTENT-ST}+ "}" |
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843 CONTENT-ST = (FILTER | URIBL | IGNORE | TLD | HTML-TAGS | HTML-LIMIT | |
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844 HOST-LIMIT | SPAMASS | REQUIRE | DCCGREY | DCCBULK | DKIM_SIGNER | |
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845 DKIM_FROM) ";" |
| 124 | 846 FILTER = "filter" DNSPREFIX ERROR-MSG2 |
| 847 URIBL = "uribl" DNSPREFIX ERROR-MSG3 | |
| 108 | 848 IGNORE = "ignore" "{" {HOSTNAME [";"]}+ "}" |
| 849 TLD = "tld" "{" {TLD [";"]}+ "}" | |
| 850 HTML-TAGS = "html_tags" "{" {HTMLTAG [";"]}+ "}" | |
| 124 | 851 ERROR-MSG1 = string containing exactly two %s replacement tokens |
| 852 both are replaced with the client ip address | |
| 853 ERROR-MSG2 = string containing exactly two %s replacement tokens | |
| 854 the first is replaced with the hostname, and the second | |
| 855 is replaced with the ip address | |
| 856 ERROR-MSG3 = string containing exactly two %s replacement tokens | |
| 857 both are replaced with the hostname | |
| 108 | 858 |
| 859 HTML-LIMIT = "html_limit" ("on" INTEGER ERROR-MSG | "off") | |
| 860 | |
| 111 | 861 HOST-LIMIT = "host_limit" ("on" INTEGER ERROR-MSG | "off" | |
| 862 "soft" INTEGER) | |
| 178 | 863 SPAMASS = "spamassassin" INTEGER |
| 864 REQUIRE = "require_match" ("yes" | "no") | |
| 865 DCCGREY = "dcc_greylist" ("yes" | "no") | |
| 866 DCCBULK = "dcc_bulk_threshold" (INTEGER | "many" | "off") | |
| 94 | 867 |
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868 DKIMSIGNER = "dkim_signer" "{" {SIGNING_DOMAIN DEF [";"]}+ "}" |
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869 DKIMFROM = "dkim_from" "{" {HEADER_FROM_DOMAIN DKIMVALUE SIGNERS [";"]}+ "}" |
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870 DKIMVALUE = "signed_white" | "signed_black" | "require_signed" | "unsigned_black" |
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871 SIGNERS = quoted comma separated SIGNING_DOMAINs no whitespace |
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872 |
| 108 | 873 ENV-TO = "env_to" "{" {(TO-ADDR | DCC-TO)}+ "}" |
| 874 TO-ADDR = ADDRESS [";"] | |
| 875 DCC-TO = "dcc_to" ("ok" | "many") "{" DCCINCLUDEFILE "}" ";" | |
| 876 | |
| 877 VERIFY = "verify" HOSTNAME ";" | |
| 168 | 878 GENERIC = "generic" REGULAREXPRESSION ERROR-MSG4 ";" |
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879 W-REGEX = "white_regex" REGULAREXPRESSION ";" |
| 168 | 880 ERROR-MSG4 = string containing exactly one %s replacement token |
| 881 which is replaced with the client name | |
| 153 | 882 AUTOWHITE = "autowhite" DAYS FILENAME ";" |
| 108 | 883 |
| 884 ENV_FROM = "env_from" [DEFAULT] "{" {(FROM-ADDR | DCC-FROM)}+ "}" | |
| 885 FROM-ADDR = ADDRESS VALUE [";"] | |
| 886 DCC-FROM = "dcc_from" "{" DCCINCLUDEFILE "}" ";" | |
| 136 | 887 |
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888 RATE-LIMIT = "rate_limit" DEFAULT_RCPT_LIMIT DAILY_MULTIPLE_RCPT |
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889 DEFAULT_IP_LIMIT DAILY_MULTIPLE_IP "{" (RATE)+ "}" |
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890 RATE = USER RCPTLIMIT IPLIMIT ";" |
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891 RCPTLIMIT = INTEGER |
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892 DEFAULT_RCPT_LIMIT = INTEGER |
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893 DAILY_MULTIPLE_RCPT = INTEGER |
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894 DEFAULT_IP_LIMIT = INTEGER |
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895 DAILY_MULTIPLE_IP = INTEGER |
| 136 | 896 |
|
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897 DEF = ("white" | "black" | "unknown") |
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898 DEFAULT = (DEF | "inherit" | "") |
| 108 | 899 ADDRESS = (USER@ | DOMAIN | USER@DOMAIN) |
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900 VALUE = (DEF | "inherit" | CHILD-CONTEXT-NAME)]]></literallayout> |
| 108 | 901 </refsect1> |
| 94 | 902 |
| 108 | 903 <refsect1 id='sample.5'> |
| 904 <title>Sample</title> | |
| 905 <literallayout class="monospaced"><![CDATA[ | |
| 127 | 906 context main-default { |
| 907 // outbound dnsbl filtering to catch our own customers that end up on the sbl | |
| 908 dnsbl sbl sbl-xbl.spamhaus.org "Mail from %s rejected - sbl; see http://www.spamhaus.org/query/bl?ip=%s"; | |
| 174 | 909 dnsbl_list sbl; |
| 127 | 910 |
| 911 // outbound content filtering to prevent our own customers from sending spam | |
| 912 content on { | |
| 913 filter sbl-xbl.spamhaus.org "Mail containing %s rejected - sbl; see http://www.spamhaus.org/query/bl?ip=%s"; | |
|
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914 uribl multi.surbl.org "Mail containing %s rejected - surbl; see http://www.surbl.org/surbl-analysis?d=%s"; |
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915 #uribl multi.uribl.com "Mail containing %s rejected - uribl; see http://l.uribl.com/?d=%s"; |
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916 #uribl dbl.spamhaus.org "Mail containing %s rejected - dbl; see http://www.spamhaus.org/query/domain?domain=%s"; |
| 127 | 917 ignore { include "hosts-ignore.conf"; }; |
| 918 tld { include "tld.conf"; }; | |
| 919 html_tags { include "html-tags.conf"; }; | |
| 920 html_limit on 20 "Mail containing excessive bad html tags rejected"; | |
| 921 html_limit off; | |
| 922 host_limit on 20 "Mail containing excessive host names rejected"; | |
| 923 host_limit soft 20; | |
| 178 | 924 spamassassin 4; |
| 925 require_match yes; | |
| 926 dcc_greylist yes; | |
| 927 dcc_bulk_threshold 50; | |
| 127 | 928 }; |
| 929 | |
|
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930 // backscatter prevention - do not send bounces for mail that we accepted but could not forward |
| 127 | 931 // we only send bounces to our own customers |
| 932 env_from unknown { | |
| 933 "<>" black; | |
| 934 }; | |
| 136 | 935 |
|
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936 // hourly recipient rate limit by smtp auth client id, or unauthenticated mail from address |
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937 // hourly unique ip addresses by smtp auth client id, or unauthenticated mail from address |
|
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938 // default hourly recipient rate limit is 30 |
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939 // daily recipient rate limits are 4 times the hourly limit |
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940 // default hourly unique ip addresses is 5 |
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941 // daily unique ip addresses are 4 times the hourly limit |
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942 rate_limit 30 4 5 4 { // default |
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943 fred 100 10; // override default limits |
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944 joe 10 2; // "" |
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945 "sam@somedomain.tld" 500 2; |
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946 "@otherdomain.tld" 100 2; |
| 136 | 947 }; |
| 127 | 948 }; |
| 949 | |
| 171 | 950 context main { |
| 951 dnsbl localp partial.blackholes.five-ten-sg.com "Mail from %s rejected - local; see http://www.five-ten-sg.com/blackhole.php?%s"; | |
| 108 | 952 dnsbl local blackholes.five-ten-sg.com "Mail from %s rejected - local; see http://www.five-ten-sg.com/blackhole.php?%s"; |
| 174 | 953 dnsbl sbl zen.spamhaus.org "Mail from %s rejected - sbl; see http://www.spamhaus.org/query/bl?ip=%s"; |
| 108 | 954 dnsbl xbl xbl.spamhaus.org "Mail from %s rejected - xbl; see http://www.spamhaus.org/query/bl?ip=%s"; |
| 249 | 955 dnswl dnswl.org list.dnswl.org 2; |
| 171 | 956 dnsbl_list local sbl; |
| 249 | 957 dnswl_list dnswl.org; |
|
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958 require_rdns yes; |
| 94 | 959 |
| 108 | 960 content on { |
|
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961 dkim_signer { |
|
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962 # |
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963 # anything signed by this is accepted. |
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964 accounts.google.com white; |
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965 }; |
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966 dkim_from { |
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967 # |
|
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968 # dmarc enforcement |
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969 aim.com unsigned_black "aim.com,mx.aim.com"; |
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970 aol.com unsigned_black "aol.com,mx.aol.com"; |
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971 yahoo.co.uk unsigned_black yahoo.co.uk; |
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972 yahoo.com unsigned_black yahoo.com; |
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973 yahoo.in unsigned_black yahoo.in; |
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974 # |
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975 # white/blacklisting based on presence of valid signatures |
|
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976 credit.paypal.com require_signed credit.paypal.com; |
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977 paypal.com require_signed paypal.com; |
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978 dhl.com require_signed dhl.com; |
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979 adp.com require_signed "adp.com,bmi.adp.com"; |
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980 # |
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981 # blacklisting based on header from value - requiring signatures |
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982 # from an impossible signer. |
|
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983 spammer.domain require_signed .; |
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984 # |
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985 # whitelisting based on strong spf pass - whitelisted if signed by |
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986 # an impossible signer (which will never happen) or strong spf pass. |
|
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987 some.domain signed_white .; |
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988 # |
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989 # whitelisting based on valid signature or strong spf pass. |
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990 # some paychex mail is signed, some is unsigned but passes strong spf. |
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991 paychex.com require_signed paychex.com; |
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992 # |
|
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993 # whitelisting from mailchimp which needs wildcards |
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994 princetheater.org require_signed "mandrillapp.com,*.mcsignup.com,*.mcsv.net,*.rsgsv.net,*.mcdlv.net"; |
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995 # |
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996 }; |
| 108 | 997 filter sbl-xbl.spamhaus.org "Mail containing %s rejected - sbl; see http://www.spamhaus.org/query/bl?ip=%s"; |
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998 uribl multi.surbl.org "Mail containing %s rejected - surbl; see http://www.surbl.org/surbl-analysis?d=%s"; |
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999 #uribl multi.uribl.com "Mail containing %s rejected - uribl; see http://l.uribl.com/?d=%s"; |
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1000 #uribl dbl.spamhaus.org "Mail containing %s rejected - dbl; see http://www.spamhaus.org/query/domain?domain=%s"; |
| 108 | 1001 ignore { include "hosts-ignore.conf"; }; |
| 1002 tld { include "tld.conf"; }; | |
| 1003 html_tags { include "html-tags.conf"; }; | |
| 1004 html_limit off; | |
| 1005 host_limit soft 20; | |
| 178 | 1006 spamassassin 5; |
| 1007 require_match yes; | |
| 1008 dcc_greylist yes; | |
| 1009 dcc_bulk_threshold 20; | |
| 108 | 1010 }; |
| 94 | 1011 |
|
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1012 generic "^dsl.static.*ttnet.net.tr$|(^|[x.-])(ppp|h|host)?([0-9]{1,3}[x.-](Red-|dynamic[x.-])?){4}" |
| 171 | 1013 "your mail server %s seems to have a generic name"; |
| 1014 | |
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1015 white_regex "=example.com=user@yourhostingaccount.com$"; |
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1016 |
| 108 | 1017 env_to { |
| 171 | 1018 # !! replace this with your domain names |
| 108 | 1019 # child contexts are not allowed to specify recipient addresses outside these domains |
| 179 | 1020 # if this is a backup-mx, you need to include here domains for which you relay to the primary mx |
| 174 | 1021 include "/etc/mail/local-host-names"; |
| 108 | 1022 }; |
| 94 | 1023 |
| 108 | 1024 context whitelist { |
| 1025 content off {}; | |
| 1026 env_to { | |
| 171 | 1027 # dcc_to ok { include "/var/dcc/whitecommon"; }; |
| 108 | 1028 }; |
| 1029 env_from white {}; # white forces all unmatched from addresses (everyone in this case) to be whitelisted | |
| 1030 # so all mail TO these env_to addresses is accepted | |
| 1031 }; | |
| 94 | 1032 |
| 171 | 1033 context abuse { |
| 1034 dnsbl_list xbl; | |
| 1035 content off {}; | |
| 174 | 1036 generic "^$ " " "; # regex cannot match, to disable generic rdns rejects |
| 171 | 1037 env_to { |
| 1038 abuse@ # no content filtering on abuse reports | |
| 1039 postmaster@ # "" | |
| 1040 }; | |
| 1041 env_from unknown {}; # ignore all parent white/black listing | |
| 1042 }; | |
| 1043 | |
| 108 | 1044 context minimal { |
| 171 | 1045 dnsbl_list sbl; |
| 178 | 1046 content on { |
| 1047 spamassassin 10; | |
| 1048 dcc_bulk_threshold many; | |
| 1049 }; | |
| 171 | 1050 generic "^$ " " "; # regex cannot match, to disable generic rdns rejects |
| 108 | 1051 env_to { |
| 1052 }; | |
| 1053 }; | |
| 94 | 1054 |
| 108 | 1055 context blacklist { |
|
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1056 dnsbl_list ; |
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1057 dnswl_list ; |
| 108 | 1058 env_to { |
| 171 | 1059 # dcc_to many { include "/var/dcc/whitecommon"; }; |
| 108 | 1060 }; |
| 1061 env_from black {}; # black forces all unmatched from addresses (everyone in this case) to be blacklisted | |
| 1062 # so all mail TO these env_to addresses is rejected | |
| 1063 }; | |
| 94 | 1064 |
| 171 | 1065 env_from unknown { |
| 1066 abuse@ abuse; # replies to abuse reports use the abuse context | |
| 1067 # dcc_from { include "/var/dcc/whitecommon"; }; | |
| 108 | 1068 }; |
| 1069 | |
| 171 | 1070 autowhite 90 "autowhite/my-auto-whitelist"; |
| 1071 # install should create /etc/dnsbl/autowhite writable by userid dnsbl | |
| 108 | 1072 };]]></literallayout> |
| 1073 </refsect1> | |
| 94 | 1074 |
| 111 | 1075 <refsect1 id='version.5'> |
|
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1076 <title>Version</title> |
| 108 | 1077 <para> |
|
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1078 @VERSION@ |
| 108 | 1079 </para> |
| 1080 </refsect1> | |
| 1081 | |
| 1082 </refentry> | |
| 1083 </reference> |