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| author | Carl Byington <carl@five-ten-sg.com> |
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| date | Thu, 07 Dec 2017 08:09:37 -0800 |
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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>2017-11-03</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 |
|
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395 listed in the current (or parents) filtering contexts dkim_from with |
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396 "required_signed", we downgrade this white answer to unknown. |
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397 If the answer is still white, mail to this recipient is accepted and the dns |
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398 lists are not checked. |
| 111 | 399 </para></listitem> |
| 400 <listitem><para> | |
| 108 | 401 If the answer is unknown, we don't reject yet, but the dns lists will be |
| 402 checked, and the content may be scanned. | |
| 111 | 403 </para></listitem> |
| 404 <listitem><para> | |
| 108 | 405 If the answer is inherit, we repeat the envelope from search in the |
| 406 parent context. | |
| 111 | 407 </para></listitem> |
| 408 <listitem><para> | |
|
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409 If the mail has not been accepted or rejected yet, and the filtering |
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410 context (or any ancestor context) specifies a non-empty whitelist regular |
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411 expression, then we check the envelope from value against that regex. |
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412 The mail is accepted if the envelope from value matches the specified regular |
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413 expression. |
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414 </para></listitem> |
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415 <listitem><para> |
| 249 | 416 If the mail has not been accepted or rejected yet, the dns white lists |
| 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, | |
| 461 we add the recipient to that auto whitelist file. This will prevent reply | |
| 462 messages from being blocked by the dnsbl or content filtering. | |
| 463 </para> | |
| 464 <para> | |
|
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465 If the mail is from localhost we skip the following dkim checks, since |
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466 such mail will never be dkim signed. This is typically mail that is generated by |
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467 apache forms. |
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468 </para> |
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469 <para> |
|
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470 If content filtering is enabled for this body, we look for dkim_signer |
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471 and dkim_from sections in the current context and parents. We collect the |
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472 signers of this message from the header added by the dkim-milter. If any |
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473 of the message signers are whitelisted, the message is accepted. |
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474 </para> |
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475 <para> |
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476 If the header from domain maps to required_signed then: |
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477 If any of the message signers are in that list, the message is accepted. |
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478 If the source ip address passes a strong spf check for the header from |
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479 domain, the message is accepted. Otherwise, the message is rejected. |
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480 </para> |
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481 <para> |
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482 If the header from domain maps to signed_white then: |
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483 If any of the message signers are in that list, the message is accepted. |
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484 If the source ip address passes a strong spf check for the header from |
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485 domain, the message is accepted. Otherwise, processing continues. |
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486 </para> |
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487 <para> |
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488 If the header from domain maps to signed_black then: |
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489 If any of the message signers are in that list, the message is rejected. |
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490 Otherwise, processing continues. |
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491 </para> |
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492 <para> |
|
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493 If any of the message signers are blacklisted, the message is rejected. |
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395
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494 </para> |
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495 <para> |
| 108 | 496 If content filtering is enabled for this body, the mail text is decoded |
| 119 | 497 (uuencode, base64, mime, html entity, url encodings), and scanned for HTTP |
| 498 and HTTPS URLs or bare host names. Hostnames must be either ip address | |
| 499 literals, or must end in a string defined by the TLD list. The first | |
| 500 <configurable> host names are checked as follows. | |
| 501 </para> | |
| 502 <para> | |
| 503 The only known list that is suitable for the content filter DNSBL is the | |
| 504 SBL. If the content filter DNSBL is defined, and any of those host | |
| 505 names resolve to ip addresses that are on that DNSBL (or have | |
| 506 nameservers that are on that list), and the host name is not on the | |
| 507 <configurable> ignore list, the mail is rejected. | |
| 508 </para> | |
| 509 <para> | |
| 510 If the content uribl DNSBL is defined, and any of those host names are | |
| 511 on that DNSBL, and the host name is not on the <configurable> | |
|
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512 ignore list, the mail is rejected. There are three lists that are suitable |
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513 here, URIBL, SURBL, and DBL. |
| 119 | 514 </para> |
| 515 <para> | |
|
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516 If any non-whitelisted recipient has a filtering context with a non-zero |
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517 spamassassin limit, then the message is passed thru spamassassin (via |
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518 spamc), and the message is rejected for those recipients with spamassassin |
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519 limits less than the resulting spamassassin score. For example, a |
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|
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521 of four or greater. If the filtering context has a spamassassin limit of |
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522 zero, then spamassassin is not called (or if called the results are not used) |
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523 for this recipient. |
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524 </para> |
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525 <para> |
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526 If any non-whitelisted recipient has a filtering context that specifies |
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527 DCC greylisting, then the message is passed thru the DCC bulk detector, |
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528 and the message is greylisted (for all recipients) if the DCC says this |
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529 message should be delayed. |
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530 </para> |
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531 <para> |
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532 If any non-whitelisted recipient has a filtering context with a non-zero |
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533 DCC bulk threshold, then the message is passed thru the DCC bulk detector, |
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534 and the message is rejected for those recipients with DCC thresholds less |
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535 than or equal to the DCC bulk score. |
| 163 | 536 </para> |
| 537 <para> | |
| 119 | 538 We also scan for excessive bad html tags, and if a <configurable> |
| 539 limit is exceeded, the mail is rejected. | |
| 108 | 540 </para> |
| 541 </refsect1> | |
| 94 | 542 |
|
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543 <refsect1 id='dmarc.1'> |
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544 <title>DMARC vs dkim_from require_signed</title> |
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545 <para> |
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546 Note that DNSBL does not implement rfc7489 DMARC. We do not look for |
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547 _dmarc.$DOMAIN txt records. |
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548 </para> |
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549 <para> |
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550 The restrictions imposed by require_signed are similar but not |
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551 identical to a DMARC reject policy with strict identifier alignment. |
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552 When doing SPF fallback, DMARC checks SPF based on the rfc5321 |
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553 envelope from domain. DNSBL checks SPF based on the rfc5322 header |
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426
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554 from domain. |
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409
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555 DMARC does not allow mail from good.example.com to be |
|
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556 signed by trusted.example.net - which is a common case. Both Microsoft |
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557 Office365 and Google run mail for customer domains, but use DKIM |
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558 signing domains in onmicrosoft.com and gappssmtp.com, which are |
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559 unrelated to the customer domain. DMARC in the default relaxed |
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560 alignment mode allows evil.example.com to sign mail from |
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561 good.example.com. DNSBL specifies the exact list of acceptable signing |
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562 domains, rather than inferring it from child/parent relationships, or |
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563 using public |
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564 suffix lists to find the organizational domain. We can block mail |
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565 from marketing.example.com while accepting mail from |
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566 billing.example.com, even if both are DKIM signed by example.com. |
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567 </para> |
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568 <para> |
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569 Suppose we have: |
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570 <literallayout class="monospaced"><![CDATA[ |
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571 rfc5321 envelope from = one@evil.example.com |
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572 rfc5322 header from = two@good.example.com |
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573 authentication results = dkim pass header.d=other.example.com |
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574 _dmarc.good.example.com txt = "v=DMARC1; p=reject; adkim:s aspf:s" |
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575 dkim_from {good.example.com require_signed other.example.com;} |
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576 ]]></literallayout> |
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577 DMARC would fail the strict identifier alignment. DNSBL allows |
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578 us to require DKIM signatures that are unrelated |
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579 to the rfc5322 header from, so we accept this message. |
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580 </para> |
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581 <para> |
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582 Suppose we have: |
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583 <literallayout class="monospaced"><![CDATA[ |
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584 rfc5321 envelope from = one@evil.example.com |
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585 rfc5322 header from = two@good.example.com |
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586 authentication results = dkim pass header.d=other.example.net |
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587 _dmarc.good.example.com txt = "v=DMARC1; p=reject; adkim:r aspf:r" |
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588 dkim_from {good.example.com require_signed other.example.net;} |
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589 ]]></literallayout> |
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590 DMARC would pass the relaxed spf identifier alignments, |
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591 and would check the evil.example.com spf record. If that |
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592 allowed the source ip, DMARC would accept the message. |
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593 DMARC would not check DKIM since example.com and example.net |
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594 do not pass even the relaxed identifer alignment requirement. |
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595 DNSBL allows us to require DKIM signatures that are not |
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596 related to the rfc5322 header from domain, so we accept |
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597 the message based on the DKIM signature and don't need to |
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598 fall back to SPF. |
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599 </para> |
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600 <para> |
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601 Suppose we have: |
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602 <literallayout class="monospaced"><![CDATA[ |
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603 rfc5321 envelope from = one@evil.example.com |
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604 rfc5322 header from = two@good.example.com |
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605 authentication results = dkim fail header.d=other.example.net |
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606 _dmarc.good.example.com txt = "v=DMARC1; p=reject; adkim:r aspf:r" |
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607 evil.example.com txt = "v=spf1 ... including the source ip |
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608 good.example.com txt = "v=spf1 ... not including the source ip |
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609 dkim_from {good.example.com require_signed other.example.net;} |
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610 ]]></literallayout> |
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611 DNSBL allows us to require DKIM signatures that are not |
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612 related to the rfc5322 header from domain. In this case |
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613 the signature fails, so we fall back to an SPF check. |
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614 We check SPF based on the rfc5322 header from, and |
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615 good.example.com does not allow the source ip, so we reject |
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616 this message. |
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617 DMARC would accept that message based on the SPF check |
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618 for evil.example.com |
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619 </para> |
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620 </refsect1> |
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621 |
| 111 | 622 <refsect1 id='access.1'> |
| 108 | 623 <title>Sendmail access vs. DNSBL</title> |
| 624 <para> | |
| 625 With the standard sendmail.mc dnsbl FEATURE, the dnsbl checks may be | |
| 626 suppressed by entries in the /etc/mail/access database. For example, | |
| 627 suppose you control a /18 of address space, and have allocated some /24s | |
| 628 to some clients. You have access entries like | |
| 111 | 629 <literallayout class="monospaced"><![CDATA[ |
| 630 192.168.4 OK | |
| 631 192.168.17 OK]]></literallayout> | |
| 108 | 632 </para> |
| 633 <para> | |
| 634 to allow those clients to smarthost thru your mail server. Now if one | |
| 635 of those clients happens get infected with a virus that turns a machine | |
| 636 into an open proxy, and their 192.168.4.45 lands on the SBL-XBL, you | |
| 637 will still wind up allowing that infected machine to smarthost thru your | |
| 638 mail servers. | |
| 639 </para> | |
| 640 <para> | |
| 641 With this DNSBL milter, the sendmail access database cannot override the | |
| 642 dnsbl checks, so that machine won't be able to send mail to or thru your | |
| 643 smarthost mail server (unless the virus/proxy can use smtp-auth). | |
| 644 </para> | |
| 645 <para> | |
| 646 Using the standard sendmail features, you would add access entries to | |
| 647 allow hosts on your local network to relay thru your mail server. Those | |
| 648 OK entries in the sendmail access database will override all the dnsbl | |
| 649 checks. With this DNSBL milter, you will need to have the local users | |
| 650 authenticate with smtp-auth to get the same effect. You might find | |
| 651 <ulink | |
| 652 url="http://www.ists.dartmouth.edu/classroom/sendmail-ssl-how-to.php"> | |
| 653 these directions</ulink> helpful for setting up smtp-auth if you are on | |
| 654 RH Linux. | |
| 655 </para> | |
| 656 </refsect1> | |
| 94 | 657 |
| 111 | 658 <refsect1 id='performance.1'> |
| 108 | 659 <title>Performance Issues</title> |
| 660 <para> | |
| 661 Consider a high volume high performance machine running sendmail. Each | |
| 662 sendmail process can do its own dns resolution. Typically, such dns | |
| 663 resolver libraries are not thread safe, and so must be protected by some | |
| 664 sort of mutex in a threaded environment. When we add a milter to | |
| 665 sendmail, we now have a collection of sendmail processes, and a | |
| 666 collection of milter threads. | |
| 667 </para> | |
| 668 <para> | |
| 669 We will be doing a lot of dns lookups per mail message, and at least | |
| 670 some of those will take many tens of seconds. If all this dns work is | |
| 671 serialized inside the milter, we have an upper limit of about 25K mail | |
| 672 messages per day. That is clearly not sufficient for many sites. | |
| 673 </para> | |
| 674 <para> | |
| 675 Since we want to do parallel dns resolution across those milter threads, | |
| 676 we add another collection of dns resolver processes. Each sendmail | |
| 677 process is talking to a milter thread over a socket, and each milter | |
| 678 thread is talking to a dns resolver process over another socket. | |
| 679 </para> | |
| 680 <para> | |
| 681 Suppose we are processing 20 messages per second, and each message | |
| 682 requires 20 seconds of dns work. Then we will have 400 sendmail | |
| 683 processes, 400 milter threads, and 400 dns resolver processes. Of | |
| 684 course that steady state is very unlikely to happen. | |
| 685 </para> | |
| 686 </refsect1> | |
| 94 | 687 |
| 688 | |
| 111 | 689 <refsect1 id='rejected.1'> |
| 108 | 690 <title>Rejected Ideas</title> |
| 691 <para> | |
| 692 The following ideas have been considered and rejected. | |
| 693 </para> | |
| 694 <para> | |
| 111 | 695 Add max_recipients setting to the context configuration. Recipients in |
| 696 excess of that limit will be rejected, and all the non-whitelisted | |
| 697 recipients will be removed. Current spammers *very* rarely send more | |
| 698 than ten recipients in a single smtp transaction, so this won't stop any | |
| 108 | 699 significant amount of spam. |
| 700 </para> | |
| 701 <para> | |
| 702 Add poison addresses to the configuration. If any recipient is | |
| 703 poison, all recipients are rejected even if they would be whitelisted, | |
| 704 and the data is rejected if sent. I have a collection of spam trap | |
| 705 addresses that would be suitable for such use. Based on my log files, | |
| 706 any mail to those spam trap addresses is rejected based on either dnsbl | |
| 707 lookups or the DCC. So this won't result in blocking any additional | |
| 708 spam. | |
| 709 </para> | |
| 710 <para> | |
| 711 Add an option to only allow one recipient if the return path is | |
| 712 empty. Based on my log files, there is no mail that violates this | |
| 713 check. | |
| 714 </para> | |
| 715 <para> | |
| 716 Reject the mail if the envelope from domain name contains any MX | |
| 717 records pointing to 127.0.0.0/8. I don't see any significant amount of | |
| 718 spam sent with such domain names. | |
| 719 </para> | |
| 720 </refsect1> | |
| 94 | 721 |
| 108 | 722 <refsect1 id='todo.1'> |
| 723 <title>TODO</title> | |
| 724 <para> | |
| 725 The following ideas are under consideration. | |
| 726 </para> | |
| 727 <para> | |
|
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728 More complete SPF check. |
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729 </para> |
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730 <para> |
| 276 | 731 Add config switch to require the HELO argument to resolve to an ip address. |
| 732 </para> | |
| 733 <para> | |
|
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734 Add white/unknown to config for smtp authenticated connections. Currently |
|
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735 any authenticated connection is fully whitelisted. The only spam control |
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736 on those connections is rate limiting. This feature would allow content based |
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737 spam controls to be applied even to authenticated connections. Add |
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738 context/authenticated_dnsbl_list and context/content/authenticated. |
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739 </para> |
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740 <para> |
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741 Add an optional list of domains to be enforced on the env_from value for |
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742 authenticated connections. User abc could be restricted to envelope from |
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743 values of a.com and b.com, user def could be restricted to envelope from |
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744 values of dd.com and ee.com. |
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745 </para> |
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746 <para> |
| 115 | 747 Look for href="hostname/path" strings that are missing the required |
| 748 http:// protocol header. Such references are still clickable in common | |
| 749 mail software. | |
| 750 </para> | |
| 108 | 751 </refsect1> |
| 94 | 752 |
| 111 | 753 <refsect1 id='copyright.1'> |
| 108 | 754 <title>Copyright</title> |
| 755 <para> | |
|
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756 Copyright (C) 2012 by 510 Software Group <carl@five-ten-sg.com> |
| 108 | 757 </para> |
| 758 <para> | |
| 759 This program is free software; you can redistribute it and/or modify it | |
| 760 under the terms of the GNU General Public License as published by the | |
| 160 | 761 Free Software Foundation; either version 3, or (at your option) any |
| 108 | 762 later version. |
| 763 </para> | |
| 764 <para> | |
| 765 You should have received a copy of the GNU General Public License along | |
| 766 with this program; see the file COPYING. If not, please write to the | |
| 767 Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. | |
| 768 </para> | |
| 769 </refsect1> | |
| 94 | 770 |
| 111 | 771 <refsect1 id='version.1'> |
|
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772 <title>Version</title> |
| 108 | 773 <para> |
|
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774 @VERSION@ |
| 108 | 775 </para> |
| 776 </refsect1> | |
| 777 </refentry> | |
| 778 | |
| 779 | |
| 780 <refentry id="@PACKAGE@.conf.5"> | |
| 781 <refentryinfo> | |
|
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782 <date>2017-11-03</date> |
|
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783 <author> |
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784 <firstname>Carl</firstname> |
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785 <surname>Byington</surname> |
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786 <affiliation><orgname>510 Software Group</orgname></affiliation> |
|
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787 <personblurb><para></para></personblurb> |
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788 </author> |
| 108 | 789 </refentryinfo> |
| 94 | 790 |
| 108 | 791 <refmeta> |
| 792 <refentrytitle>@PACKAGE@.conf</refentrytitle> | |
| 793 <manvolnum>5</manvolnum> | |
| 794 <refmiscinfo>@PACKAGE@ @VERSION@</refmiscinfo> | |
| 795 </refmeta> | |
| 94 | 796 |
| 108 | 797 <refnamediv id='name.5'> |
| 798 <refname>@PACKAGE@.conf</refname> | |
| 111 | 799 <refpurpose>configuration file for @PACKAGE@ sendmail milter</refpurpose> |
| 108 | 800 </refnamediv> |
| 801 | |
| 802 <refsynopsisdiv id='synopsis.5'> | |
| 803 <title>Synopsis</title> | |
| 804 <cmdsynopsis> | |
| 805 <command>@PACKAGE@.conf</command> | |
| 806 </cmdsynopsis> | |
| 807 </refsynopsisdiv> | |
| 94 | 808 |
| 108 | 809 <refsect1 id='description.5'> |
| 810 <title>Description</title> | |
| 811 <para>The <command>@PACKAGE@.conf</command> configuration file is | |
|
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812 specified by this partial bnf description. Comments start with // |
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813 or # and extend to the end of the line. To include the contents |
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814 of some file verbatim in the dnsbl.conf file, use |
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815 <literallayout class="monospaced"><![CDATA[include "<file>";]]></literallayout> |
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816 </para> |
| 108 | 817 |
| 818 <literallayout class="monospaced"><![CDATA[ | |
| 819 CONFIG = {CONTEXT ";"}+ | |
| 820 CONTEXT = "context" NAME "{" {STATEMENT}+ "}" | |
|
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821 STATEMENT = ( DNSBL | DNSBLLIST | DNSWL | DNSWLLIST | CONTENT | ENV-TO |
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822 | VERIFY | GENERIC | W_REGEX | AUTOWHITE | CONTEXT | ENV-FROM |
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823 | RATE-LIMIT | REQUIRERDNS) ";" |
| 108 | 824 |
| 124 | 825 DNSBL = "dnsbl" NAME DNSPREFIX ERROR-MSG1 |
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826 DNSBLLIST = "dnsbl_list" {NAME}* |
| 108 | 827 |
|
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828 DNSWL = "dnswl" NAME DNSPREFIX LEVEL |
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829 DNSWLLIST = "dnswl_list" {NAME}* |
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830 LEVEL = INTEGER |
| 94 | 831 |
|
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832 REQUIRERDNS = "require_rdns" ("yes" | "no") |
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833 |
| 108 | 834 CONTENT = "content" ("on" | "off") "{" {CONTENT-ST}+ "}" |
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835 CONTENT-ST = (FILTER | URIBL | IGNORE | TLD | HTML-TAGS | HTML-LIMIT | |
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836 HOST-LIMIT | SPAMASS | REQUIRE | DCCGREY | DCCBULK | DKIM_SIGNER | |
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837 DKIM_FROM) ";" |
| 124 | 838 FILTER = "filter" DNSPREFIX ERROR-MSG2 |
| 839 URIBL = "uribl" DNSPREFIX ERROR-MSG3 | |
| 108 | 840 IGNORE = "ignore" "{" {HOSTNAME [";"]}+ "}" |
| 841 TLD = "tld" "{" {TLD [";"]}+ "}" | |
| 842 HTML-TAGS = "html_tags" "{" {HTMLTAG [";"]}+ "}" | |
| 124 | 843 ERROR-MSG1 = string containing exactly two %s replacement tokens |
| 844 both are replaced with the client ip address | |
| 845 ERROR-MSG2 = string containing exactly two %s replacement tokens | |
| 846 the first is replaced with the hostname, and the second | |
| 847 is replaced with the ip address | |
| 848 ERROR-MSG3 = string containing exactly two %s replacement tokens | |
| 849 both are replaced with the hostname | |
| 108 | 850 |
| 851 HTML-LIMIT = "html_limit" ("on" INTEGER ERROR-MSG | "off") | |
| 852 | |
| 111 | 853 HOST-LIMIT = "host_limit" ("on" INTEGER ERROR-MSG | "off" | |
| 854 "soft" INTEGER) | |
| 178 | 855 SPAMASS = "spamassassin" INTEGER |
| 856 REQUIRE = "require_match" ("yes" | "no") | |
| 857 DCCGREY = "dcc_greylist" ("yes" | "no") | |
| 858 DCCBULK = "dcc_bulk_threshold" (INTEGER | "many" | "off") | |
| 94 | 859 |
|
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860 DKIMSIGNER = "dkim_signer" "{" {SIGNING_DOMAIN DEF [";"]}+ "}" |
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861 DKIMFROM = "dkim_from" "{" {HEADER_FROM_DOMAIN DKIMVALUE SIGNERS [";"]}+ "}" |
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862 DKIMVALUE = "signed_white" | "signed_black" | "require_signed" |
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863 SIGNERS = quoted comma separated SIGNING_DOMAINs no whitespace |
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864 |
| 108 | 865 ENV-TO = "env_to" "{" {(TO-ADDR | DCC-TO)}+ "}" |
| 866 TO-ADDR = ADDRESS [";"] | |
| 867 DCC-TO = "dcc_to" ("ok" | "many") "{" DCCINCLUDEFILE "}" ";" | |
| 868 | |
| 869 VERIFY = "verify" HOSTNAME ";" | |
| 168 | 870 GENERIC = "generic" REGULAREXPRESSION ERROR-MSG4 ";" |
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871 W-REGEX = "white_regex" REGULAREXPRESSION ";" |
| 168 | 872 ERROR-MSG4 = string containing exactly one %s replacement token |
| 873 which is replaced with the client name | |
| 153 | 874 AUTOWHITE = "autowhite" DAYS FILENAME ";" |
| 108 | 875 |
| 876 ENV_FROM = "env_from" [DEFAULT] "{" {(FROM-ADDR | DCC-FROM)}+ "}" | |
| 877 FROM-ADDR = ADDRESS VALUE [";"] | |
| 878 DCC-FROM = "dcc_from" "{" DCCINCLUDEFILE "}" ";" | |
| 136 | 879 |
|
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880 RATE-LIMIT = "rate_limit" DEFAULT_RCPT_LIMIT DAILY_MULTIPLE_RCPT |
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881 DEFAULT_IP_LIMIT DAILY_MULTIPLE_IP "{" (RATE)+ "}" |
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882 RATE = USER RCPTLIMIT IPLIMIT ";" |
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883 RCPTLIMIT = INTEGER |
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884 DEFAULT_RCPT_LIMIT = INTEGER |
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885 DAILY_MULTIPLE_RCPT = INTEGER |
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886 DEFAULT_IP_LIMIT = INTEGER |
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887 DAILY_MULTIPLE_IP = INTEGER |
| 136 | 888 |
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889 DEF = ("white" | "black" | "unknown") |
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890 DEFAULT = (DEF | "inherit" | "") |
| 108 | 891 ADDRESS = (USER@ | DOMAIN | USER@DOMAIN) |
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892 VALUE = (DEF | "inherit" | CHILD-CONTEXT-NAME)]]></literallayout> |
| 108 | 893 </refsect1> |
| 94 | 894 |
| 108 | 895 <refsect1 id='sample.5'> |
| 896 <title>Sample</title> | |
| 897 <literallayout class="monospaced"><![CDATA[ | |
| 127 | 898 context main-default { |
| 899 // outbound dnsbl filtering to catch our own customers that end up on the sbl | |
| 900 dnsbl sbl sbl-xbl.spamhaus.org "Mail from %s rejected - sbl; see http://www.spamhaus.org/query/bl?ip=%s"; | |
| 174 | 901 dnsbl_list sbl; |
| 127 | 902 |
| 903 // outbound content filtering to prevent our own customers from sending spam | |
| 904 content on { | |
| 905 filter sbl-xbl.spamhaus.org "Mail containing %s rejected - sbl; see http://www.spamhaus.org/query/bl?ip=%s"; | |
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906 uribl multi.surbl.org "Mail containing %s rejected - surbl; see http://www.surbl.org/surbl-analysis?d=%s"; |
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907 #uribl multi.uribl.com "Mail containing %s rejected - uribl; see http://l.uribl.com/?d=%s"; |
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908 #uribl dbl.spamhaus.org "Mail containing %s rejected - dbl; see http://www.spamhaus.org/query/domain?domain=%s"; |
| 127 | 909 ignore { include "hosts-ignore.conf"; }; |
| 910 tld { include "tld.conf"; }; | |
| 911 html_tags { include "html-tags.conf"; }; | |
| 912 html_limit on 20 "Mail containing excessive bad html tags rejected"; | |
| 913 html_limit off; | |
| 914 host_limit on 20 "Mail containing excessive host names rejected"; | |
| 915 host_limit soft 20; | |
| 178 | 916 spamassassin 4; |
| 917 require_match yes; | |
| 918 dcc_greylist yes; | |
| 919 dcc_bulk_threshold 50; | |
| 127 | 920 }; |
| 921 | |
|
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922 // backscatter prevention - do not send bounces for mail that we accepted but could not forward |
| 127 | 923 // we only send bounces to our own customers |
| 924 env_from unknown { | |
| 925 "<>" black; | |
| 926 }; | |
| 136 | 927 |
|
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928 // hourly recipient rate limit by smtp auth client id, or unauthenticated mail from address |
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929 // hourly unique ip addresses by smtp auth client id, or unauthenticated mail from address |
|
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930 // default hourly recipient rate limit is 30 |
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931 // daily recipient rate limits are 4 times the hourly limit |
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932 // default hourly unique ip addresses is 5 |
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933 // daily unique ip addresses are 4 times the hourly limit |
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934 rate_limit 30 4 5 4 { // default |
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935 fred 100 10; // override default limits |
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936 joe 10 2; // "" |
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937 "sam@somedomain.tld" 500 2; |
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938 "@otherdomain.tld" 100 2; |
| 136 | 939 }; |
| 127 | 940 }; |
| 941 | |
| 171 | 942 context main { |
| 943 dnsbl localp partial.blackholes.five-ten-sg.com "Mail from %s rejected - local; see http://www.five-ten-sg.com/blackhole.php?%s"; | |
| 108 | 944 dnsbl local blackholes.five-ten-sg.com "Mail from %s rejected - local; see http://www.five-ten-sg.com/blackhole.php?%s"; |
| 174 | 945 dnsbl sbl zen.spamhaus.org "Mail from %s rejected - sbl; see http://www.spamhaus.org/query/bl?ip=%s"; |
| 108 | 946 dnsbl xbl xbl.spamhaus.org "Mail from %s rejected - xbl; see http://www.spamhaus.org/query/bl?ip=%s"; |
| 249 | 947 dnswl dnswl.org list.dnswl.org 2; |
| 171 | 948 dnsbl_list local sbl; |
| 249 | 949 dnswl_list dnswl.org; |
|
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950 require_rdns yes; |
| 94 | 951 |
| 108 | 952 content on { |
|
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953 dkim_signer { |
|
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954 # |
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955 # anything signed by this is accepted. |
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956 accounts.google.com white; |
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957 }; |
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958 dkim_from { |
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959 # |
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960 # white/blacklisting based on presence of valid signatures |
|
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961 credit.paypal.com require_signed credit.paypal.com; |
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962 paypal.com require_signed paypal.com; |
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963 dhl.com require_signed dhl.com; |
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964 adp.com require_signed "adp.com,bmi.adp.com"; |
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965 # |
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966 # blacklisting based on header from value - requiring signatures |
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967 # from an impossible signer. |
|
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968 spammer.domain require_signed .; |
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969 # |
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970 # whitelisting based on strong spf pass - whitelisted if signed by |
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971 # an impossible signer (which will never happen) or strong spf pass. |
|
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972 some.domain signed_white .; |
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973 # |
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974 # whitelisting based on valid signature or strong spf pass. |
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975 # some paychex mail is signed, some is unsigned but passes strong spf. |
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976 paychex.com require_signed paychex.com; |
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977 # |
|
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978 # whitelisting from mailchimp which needs wildcards |
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979 princetheater.org require_signed "mandrillapp.com,*.mcsignup.com,*.mcsv.net,*.rsgsv.net,*.mcdlv.net"; |
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980 # |
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981 }; |
| 108 | 982 filter sbl-xbl.spamhaus.org "Mail containing %s rejected - sbl; see http://www.spamhaus.org/query/bl?ip=%s"; |
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983 uribl multi.surbl.org "Mail containing %s rejected - surbl; see http://www.surbl.org/surbl-analysis?d=%s"; |
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984 #uribl multi.uribl.com "Mail containing %s rejected - uribl; see http://l.uribl.com/?d=%s"; |
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985 #uribl dbl.spamhaus.org "Mail containing %s rejected - dbl; see http://www.spamhaus.org/query/domain?domain=%s"; |
| 108 | 986 ignore { include "hosts-ignore.conf"; }; |
| 987 tld { include "tld.conf"; }; | |
| 988 html_tags { include "html-tags.conf"; }; | |
| 989 html_limit off; | |
| 990 host_limit soft 20; | |
| 178 | 991 spamassassin 5; |
| 992 require_match yes; | |
| 993 dcc_greylist yes; | |
| 994 dcc_bulk_threshold 20; | |
| 108 | 995 }; |
| 94 | 996 |
|
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997 generic "^dsl.static.*ttnet.net.tr$|(^|[x.-])(ppp|h|host)?([0-9]{1,3}[x.-](Red-|dynamic[x.-])?){4}" |
| 171 | 998 "your mail server %s seems to have a generic name"; |
| 999 | |
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1000 white_regex "=example.com=user@yourhostingaccount.com$"; |
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1001 |
| 108 | 1002 env_to { |
| 171 | 1003 # !! replace this with your domain names |
| 108 | 1004 # child contexts are not allowed to specify recipient addresses outside these domains |
| 179 | 1005 # if this is a backup-mx, you need to include here domains for which you relay to the primary mx |
| 174 | 1006 include "/etc/mail/local-host-names"; |
| 108 | 1007 }; |
| 94 | 1008 |
| 108 | 1009 context whitelist { |
| 1010 content off {}; | |
| 1011 env_to { | |
| 171 | 1012 # dcc_to ok { include "/var/dcc/whitecommon"; }; |
| 108 | 1013 }; |
| 1014 env_from white {}; # white forces all unmatched from addresses (everyone in this case) to be whitelisted | |
| 1015 # so all mail TO these env_to addresses is accepted | |
| 1016 }; | |
| 94 | 1017 |
| 171 | 1018 context abuse { |
| 1019 dnsbl_list xbl; | |
| 1020 content off {}; | |
| 174 | 1021 generic "^$ " " "; # regex cannot match, to disable generic rdns rejects |
| 171 | 1022 env_to { |
| 1023 abuse@ # no content filtering on abuse reports | |
| 1024 postmaster@ # "" | |
| 1025 }; | |
| 1026 env_from unknown {}; # ignore all parent white/black listing | |
| 1027 }; | |
| 1028 | |
| 108 | 1029 context minimal { |
| 171 | 1030 dnsbl_list sbl; |
| 178 | 1031 content on { |
| 1032 spamassassin 10; | |
| 1033 dcc_bulk_threshold many; | |
| 1034 }; | |
| 171 | 1035 generic "^$ " " "; # regex cannot match, to disable generic rdns rejects |
| 108 | 1036 env_to { |
| 1037 }; | |
| 1038 }; | |
| 94 | 1039 |
| 108 | 1040 context blacklist { |
|
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1041 dnsbl_list ; |
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1042 dnswl_list ; |
| 108 | 1043 env_to { |
| 171 | 1044 # dcc_to many { include "/var/dcc/whitecommon"; }; |
| 108 | 1045 }; |
| 1046 env_from black {}; # black forces all unmatched from addresses (everyone in this case) to be blacklisted | |
| 1047 # so all mail TO these env_to addresses is rejected | |
| 1048 }; | |
| 94 | 1049 |
| 171 | 1050 env_from unknown { |
| 1051 abuse@ abuse; # replies to abuse reports use the abuse context | |
| 1052 # dcc_from { include "/var/dcc/whitecommon"; }; | |
| 108 | 1053 }; |
| 1054 | |
| 171 | 1055 autowhite 90 "autowhite/my-auto-whitelist"; |
| 1056 # install should create /etc/dnsbl/autowhite writable by userid dnsbl | |
| 108 | 1057 };]]></literallayout> |
| 1058 </refsect1> | |
| 94 | 1059 |
| 111 | 1060 <refsect1 id='version.5'> |
|
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1061 <title>Version</title> |
| 108 | 1062 <para> |
|
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1063 @VERSION@ |
| 108 | 1064 </para> |
| 1065 </refsect1> | |
| 1066 | |
| 1067 </refentry> | |
| 1068 </reference> |