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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>

 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. 

 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. 

 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. 

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

<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 query format </a>

</ul>

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

 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". Other
interfaces such as the Postfix sendmail(1) command may still accept
an "unknown" recipient. 

 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 (typically, in /etc/passwd) or
local aliases (typically, in /etc/aliases): 

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

 To turn off unknown local recipient rejects by the SMTP server,
specify: 

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

 That is, an empty value. With this setting, the Postfix SMTP
server will not reject mail with "User unknown in local recipient
table". 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. 

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

<ul>

 <li> 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. 

 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: 

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

 If you don't use the local(8) or virtual(8) 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. 

 <li> 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 recipients. 

 Solution: you need to add the database that lists the
 non-UNIX recipients: 

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

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

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

 Solution: you must disable the local_recipient_maps feature
 completely, so that the Postfix SMTP server accepts mail for
 all local addresses: 

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

</ul>

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

 If local_recipient_maps specifies local files, such as files in
postmap(1) or postalias(1) format, then the Postfix SMTP server
generates the following queries: 

<ul>

<li> The full recipient address. This query supports a non-default
local_transport setting with a delivery agent such as lmtp(8) or
virtual(8). See "<a href="#main_config">Configuring local_recipient_maps
in main.cf</a>: for additional guidance for what lookup tables to
specify. 

<li> The recipient address local-part. This query supports the
default local_transport setting with the UNIX-compatible local(8)
delivery agent; the Postfix SMTP server makes this query only when
the recipient domain matches $mydestination, $inet_interfaces or
$proxy_interfaces. 

<li> The recipient @domain. This query supports a non-default
local_transport setting with a delivery agent such as virtual(8);
it is a wildcard for domains that do not have a valid recipient
list. 

</ul>

 NOTES: 

<ul>

<li> A lookup table should return a non-empty result when the
address exists, and should return "not found" when the address does
not exist. In particular, a zero-length (empty) result does not
count as a "not found" result. 

<li> When local_recipient_maps specifies a lookup table based
on ldap:, memcache:, mongodb:, mysql:, pgsql:, sqlite:, or other
external database, then the Postfix SMTP server queries that lookup
table with the same queries as described at the start of this
section, and expects the same results. 

<li> To suppress lookups for the local-part and the
@domain wild-card, specify the domain setting in a
Postfix ldap:, memcache:, mongodb:, mysql:, pgsql:, sqlite:, etc.,
database client configuration file. 

<li> When local_recipient_maps specifies a lookup table based
on pcre:, regexp:, socketmap: or tcp:, Postfix queries that table
only with the full recipient address, and not with the local-part
or the @domain wild-card. 

</ul>

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