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<title>Rejecting Unknown Local Recipients with Postfix</title>

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<h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Rejecting Unknown Local Recipients with Postfix</h1>

<hr>

<h2>Introduction</h2>

<p> As of Postfix version 2.0, the Postfix SMTP server rejects mail
for unknown recipients in local domains (domains that match
$mydestination or the IP addresses in $inet_interfaces or
$proxy_interfaces) with "User unknown in local recipient table".
This feature was optional with earlier Postfix versions. </p>

<p> The good news is that this keeps undeliverable mail out of your
queue, so that your mail queue is not clogged up with undeliverable
MAILER-DAEMON messages. </p>

<p> The bad news is that it may cause mail to be rejected when you
upgrade from a Postfix system that was not configured to reject
mail for unknown local recipients. </p>

<p> This document describes what steps are needed in order to reject
unknown local recipients correctly. </p>

<ul>

<li><a href="#main_config">Configuring local_recipient_maps
in main.cf</a>

<li><a href="#change">When you need to change the local_recipient_maps
setting in main.cf</a>

<li><a href="#format">Local recipient table format </a>

</ul>

<h2><a name="main_config">Configuring local_recipient_maps
in main.cf</a></h2>

<p> The local_recipient_maps parameter specifies lookup tables with
all names or addresses of local recipients. A recipient address is
local when its domain matches $mydestination, $inet_interfaces or
$proxy_interfaces. If a local username or address is not listed in
$local_recipient_maps, then the Postfix SMTP server will reject
the address with "User unknown in local recipient table".  </p>

<p> The default setting, shown below, assumes that you use the
default Postfix local(8) delivery agent for local delivery, where
recipients are either UNIX accounts or local aliases: </p>

<blockquote>
<pre>
/etc/postfix/main.cf:
    local_recipient_maps = proxy:unix:passwd.byname $alias_maps
</pre>
</blockquote>

<p> To turn off unknown local recipient rejects by the SMTP server,
specify: </p>

<blockquote>
<pre>
/etc/postfix/main.cf:
    local_recipient_maps =
</pre>
</blockquote>

<p> That is, an empty value. With this setting, the Postfix SMTP
server will not reject mail with "User unknown in local recipient
table". <b> Don't do this on systems that receive mail directly
from the Internet. With today's worms and viruses, Postfix will
become a backscatter source: it accepts mail for non-existent
recipients and then tries to return that mail as "undeliverable"
to the often forged sender address</b>. </p>

<h2><a name="change">When you need to change the local_recipient_maps
setting in main.cf</a></h2>

<ul>

    <li> <p> Problem: you don't use the default Postfix local(8)
    delivery agent for domains matching $mydestination, $inet_interfaces,
    or $proxy_interfaces. For example, you redefined the
    "local_transport" setting in main.cf.  </p>

    <p> Solution: your local_recipient_maps setting needs to specify
    a database that lists all the known user names or addresses
    for that delivery agent. For example, if you deliver users in
    $mydestination etc. domains via the virtual(8) delivery agent,
    specify: </p>

<pre>
/etc/postfix/main.cf
    mydestination = $myhostname localhost.$mydomain localhost ...
    local_transport = virtual
    local_recipient_maps = $virtual_mailbox_maps
</pre>

    <p> If you use a different delivery agent for $mydestination
    etc. domains, see the section "<a href="#format">Local recipient
    table format</a>" below for a description of how the table
    should be populated.  </p>

    <li> <p> Problem: you use the mailbox_transport or fallback_transport
    feature of the Postfix local(8) delivery agent in order to
    deliver mail to non-UNIX accounts. </p>

    <p> Solution: you need to add the database that lists the
    non-UNIX users: </p>

<pre>
/etc/postfix/main.cf
    local_recipient_maps = proxy:unix:passwd.byname, $alias_maps,
        &lt;the database with non-UNIX accounts&gt;
</pre>

    <p> See the section "<a href="#format">Local recipient table
    format</a>" below for a description of how the table should be
    populated. </p>

    <li> <p> Problem: you use the luser_relay feature of the Postfix
    local delivery agent. </p>

    <p> Solution: you must disable the local_recipient_maps feature
    completely, so that Postfix accepts mail for all local addresses:
    </p>

<pre>
/etc/postfix/main.cf
    local_recipient_maps =
</pre>

</ul>

<h2><a name="format">Local recipient table format</a> </h2>

<p> If you use local files in postmap(1) format, then
local_recipient_maps expects the following table format:  </p>

<ul>

<li> <p> In the left-hand side, specify a bare username, an
"@domain.tld" wild-card, or specify a complete "user@domain.tld"
address.  </p>

<li> <p> You have to specify something on the right-hand side of
the table, but the value is ignored by local_recipient_maps.

</ul>

<p> If you use lookup tables based on NIS, LDAP, MYSQL, or PGSQL,
then local_recipient_maps does the same queries as for local files
in postmap(1) format, and expects the same results.  </p>

<p> With regular expression tables, Postfix only queries with the
full recipient address, and not with the bare username or the
"@domain.tld" wild-card. </p>

<p> NOTE: a lookup table should always return a result when the address
exists, and should always return "not found" when the address does
not exist. In particular, a zero-length result does not count as
a "not found" result. </p>

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