external/ibm-public/postfix/dist/proto/LOCAL_RECIPIENT_README.html

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   8 <title>Rejecting Unknown Local Recipients with Postfix</title>
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  16 <h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Rejecting Unknown Local Recipients with Postfix</h1>
  17
  18 <hr>
  19
  20 <h2>Introduction</h2>
  21
  22 <p> As of Postfix version 2.0, the Postfix SMTP server rejects mail
  23 for unknown recipients in local domains (domains that match
  24 $mydestination or the IP addresses in $inet_interfaces or
  25 $proxy_interfaces) with "User unknown in local recipient table".
  26 This feature was optional with earlier Postfix versions. </p>
  27
  28 <p> The good news is that this keeps undeliverable mail out of your
  29 queue, so that your mail queue is not clogged up with undeliverable
  30 MAILER-DAEMON messages. </p>
  31
  32 <p> The bad news is that it may cause mail to be rejected when you
  33 upgrade from a Postfix system that was not configured to reject
  34 mail for unknown local recipients. </p>
  35
  36 <p> This document describes what steps are needed in order to reject
  37 unknown local recipients correctly. </p>
  38
  39 <ul>
  40
  41 <li><a href="#main_config">Configuring local_recipient_maps
  42 in main.cf</a>
  43
  44 <li><a href="#change">When you need to change the local_recipient_maps
  45 setting in main.cf</a>
  46
  47 <li><a href="#format">Local recipient table format </a>
  48
  49 </ul>
  50
  51 <h2><a name="main_config">Configuring local_recipient_maps
  52 in main.cf</a></h2>
  53
  54 <p> The local_recipient_maps parameter specifies lookup tables with
  55 all names or addresses of local recipients. A recipient address is
  56 local when its domain matches $mydestination, $inet_interfaces or
  57 $proxy_interfaces. If a local username or address is not listed in
  58 $local_recipient_maps, then the Postfix SMTP server will reject
  59 the address with "User unknown in local recipient table".  </p>
  60
  61 <p> The default setting, shown below, assumes that you use the
  62 default Postfix local(8) delivery agent for local delivery, where
  63 recipients are either UNIX accounts or local aliases: </p>
  64
  65 <blockquote>
  66 <pre>
  67 /etc/postfix/main.cf:
  68     local_recipient_maps = proxy:unix:passwd.byname $alias_maps
  69 </pre>
  70 </blockquote>
  71
  72 <p> To turn off unknown local recipient rejects by the SMTP server,
  73 specify: </p>
  74
  75 <blockquote>
  76 <pre>
  77 /etc/postfix/main.cf:
  78     local_recipient_maps =
  79 </pre>
  80 </blockquote>
  81
  82 <p> That is, an empty value. With this setting, the Postfix SMTP
  83 server will not reject mail with "User unknown in local recipient
  84 table". <b> Don't do this on systems that receive mail directly
  85 from the Internet. With today's worms and viruses, Postfix will
  86 become a backscatter source: it accepts mail for non-existent
  87 recipients and then tries to return that mail as "undeliverable"
  88 to the often forged sender address</b>. </p>
  89
  90 <h2><a name="change">When you need to change the local_recipient_maps
  91 setting in main.cf</a></h2>
  92
  93 <ul>
  94
  95     <li> <p> Problem: you don't use the default Postfix local(8)
  96     delivery agent for domains matching $mydestination, $inet_interfaces,
  97     or $proxy_interfaces. For example, you redefined the
  98     "local_transport" setting in main.cf.  </p>
  99
 100     <p> Solution: your local_recipient_maps setting needs to specify
 101     a database that lists all the known user names or addresses
 102     for that delivery agent. For example, if you deliver users in
 103     $mydestination etc. domains via the virtual(8) delivery agent,
 104     specify: </p>
 105
 106 <pre>
 107 /etc/postfix/main.cf
 108     mydestination = $myhostname localhost.$mydomain localhost ...
 109     local_transport = virtual
 110     local_recipient_maps = $virtual_mailbox_maps
 111 </pre>
 112
 113     <p> If you use a different delivery agent for $mydestination
 114     etc. domains, see the section "<a href="#format">Local recipient
 115     table format</a>" below for a description of how the table
 116     should be populated.  </p>
 117
 118     <li> <p> Problem: you use the mailbox_transport or fallback_transport
 119     feature of the Postfix local(8) delivery agent in order to
 120     deliver mail to non-UNIX accounts. </p>
 121
 122     <p> Solution: you need to add the database that lists the
 123     non-UNIX users: </p>
 124
 125 <pre>
 126 /etc/postfix/main.cf
 127     local_recipient_maps = proxy:unix:passwd.byname, $alias_maps,
 128         &lt;the database with non-UNIX accounts&gt;
 129 </pre>
 130
 131     <p> See the section "<a href="#format">Local recipient table
 132     format</a>" below for a description of how the table should be
 133     populated. </p>
 134
 135     <li> <p> Problem: you use the luser_relay feature of the Postfix
 136     local delivery agent. </p>
 137
 138     <p> Solution: you must disable the local_recipient_maps feature
 139     completely, so that Postfix accepts mail for all local addresses:
 140     </p>
 141
 142 <pre>
 143 /etc/postfix/main.cf
 144     local_recipient_maps =
 145 </pre>
 146
 147 </ul>
 148
 149 <h2><a name="format">Local recipient table format</a> </h2>
 150
 151 <p> If you use local files in postmap(1) format, then
 152 local_recipient_maps expects the following table format:  </p>
 153
 154 <ul>
 155
 156 <li> <p> In the left-hand side, specify a bare username, an
 157 "@domain.tld" wild-card, or specify a complete "user@domain.tld"
 158 address.  </p>
 159
 160 <li> <p> You have to specify something on the right-hand side of
 161 the table, but the value is ignored by local_recipient_maps.
 162
 163 </ul>
 164
 165 <p> If you use lookup tables based on NIS, LDAP, MYSQL, or PGSQL,
 166 then local_recipient_maps does the same queries as for local files
 167 in postmap(1) format, and expects the same results.  </p>
 168
 169 <p> With regular expression tables, Postfix only queries with the
 170 full recipient address, and not with the bare username or the
 171 "@domain.tld" wild-card. </p>
 172
 173 <p> NOTE: a lookup table should always return a result when the address
 174 exists, and should always return "not found" when the address does
 175 not exist. In particular, a zero-length result does not count as
 176 a "not found" result. </p>
 177
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