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|
<html>
<!--Warning, preformatted content! -->
<head>
<title>Postfix Frequently Asked Questions</title>
</head>
<body>
<h1><a href="big-picture.html"><img src="small-picture.gif" width="115" height="45"></a> Postfix Frequently Asked Questions</h1>
<hr>
<a href="index.html">Up one level</a> | Postfix FAQ
<h2>Table of contents</h2>
<p>
<ul>
<li><a href="#example_config">Example configurations</a>
<li><a href="#sendmail_incompatibility">Sendmail incompatibility</a>
<li><a href="#relaying">Mail relaying</a>
<li><a href="#remote_delivery">Delivery to remote systems</a>
<li><a href="#local_delivery">Delivery to local (non-virtual) addresses</a>
<li><a href="#mailing_lists">Mailing lists</a>
<li><a href="#virtual_domains">Virtual domains</a>
<li><a href="#address_rewriting">Address rewriting</a>
<li><a href="#content_filtering">Content filtering</a>
<li><a href="#other_transports">Other transports: UUCP, FAX, etc.</a>
<li><a href="#compiling_installing">Compiling and installing Postfix</a>
</ul>
<p>
<a name="example_config"><h3>Example configurations</h3>
<ul>
<li><a href="#stand_alone">Stand-alone machine</a>
<li><a href="#workstation_server">Workstations and servers</a>
<li><a href="#null_client">Null clients</a>
<li><a href="#intranet">Running Postfix inside an intranet</a>
<li><a href="#firewall">Running Postfix on a firewall</a>
<li><a href="#dialup">Running Postfix on a dialup machine</a>
</ul>
<a name="sendmail_incompatibility"><h3>Sendmail incompatibility</h3>
<ul>
<li><a href="#verbose">Postfix breaks "sendmail -v"</a>
<li><a href="#delayed">Postfix sends no "delayed mail" notices</a>
<li><a href="#root">Root's mail is delivered to nobody</a>
<li><a href="#bogus">Postfix accepts mail for non-existing local users</a>
<li><a href="#duplicate">Postfix sends duplicate mail</a>
<li><a href="#metoo">Postfix sends mail to every member of a
distribution list</a>
<li><a href="#delivered">Getting rid of the ugly Delivered-To: header</a>
<li><a href="#majordomo-approve">Postfix breaks the majordomo "approve" command</a>
<li><a href="#worm">Postfix accepts MAIL FROM/RCPT TO "|command"</a>
</ul>
<a name="relaying"><h3>Mail relaying</h3>
<ul>
<li><a href="#open_relay">Help! Postfix is an open relay</a>
<li><a href="#mobile">Relaying mail for mobile users</a>
<li><a href="#virtual_setup">Postfix refuses mail for virtual
domains with "relay access denied"</a>
<li><a href="#relay_restrict">Restricting what users can send mail to off-site destinations</a>
</ul>
<a name="remote_delivery"><h3>Delivery to remote systems</h3>
<ul>
<li><a href="#timeouts">Mail fails consistently with timeout or lost connection</a>
</ul>
<a name="local_delivery"><h3>Delivery to local (non-virtual) addresses</h3>
<ul>
<li><a href="#root">Root's mail is delivered to nobody</a>
<li><a href="#bogus">Postfix accepts mail for non-existing local users</a>
<li><a href="#some_local">Delivering some users locally while
sending mail as user@domain</a>
<li><a href="#maildir">Support for maildir-style mailboxes</a>
<li><a href="#procmail">Using Procmail for system-wide local delivery</a>
<li><a href="#delivered">Getting rid of the ugly Delivered-To: header</a>
<li><a href="#duplicate">Postfix sends duplicate mail</a>
<li><a href="#metoo">Postfix sends mail to every member of a
distribution list</a>
</ul>
<a name="mailing_lists"><h3>Mailing lists</h3>
<ul>
<li><a href="#majordomo-approve">Postfix breaks the majordomo "approve" command</a>
<li><a href="#internal-list">Protecting internal email distribution lists</a>
<li><a href="#duplicate">Postfix sends duplicate mail</a>
<li><a href="#metoo">Postfix sends mail to every member of a
distribution list</a>
</ul>
<a name="virtual_domains"><h3>Virtual domains</h3>
<ul>
<li><a href="#virtual_setup">How to configure a Postfix virtual domain</a>
<li><a href="#virtual_setup">Postfix does not refuse mail for
unknown virtual users</a>
<li><a href="#virtual_setup">Mail for unknown virtual users fails
with "mail loops back to myself"</a>
<li><a href="#virtual_setup">Postfix refuses mail for virtual
domains with "user unknown"</a>
<li><a href="#virtual_setup">Postfix refuses mail for virtual
domains with "relay access denied"</a>
<li><a href="#command">Commands don't work in Postfix virtual maps</a>
<li><a href="#domain_mailbox">Receiving a virtual domain in a
mailbox</a>
</ul>
<a name="address_rewriting"><h3>Address rewriting</h3>
<ul>
<li><a href="#masquerade">Address masquerading with exceptions</a>
</ul>
<a name="content_filtering"><h3>Content filtering</h3>
<ul>
<li><a href="#scanning">Support for virus scanning</a>
</ul>
<a name="other_transports"><h3>Other transports: UUCP, FAX, etc.</h3>
<ul>
<li><a href="#internet-uucp">Setting up an Internet to UUCP gateway</a>
<li><a href="#uucp-only">Using UUCP as the default transport</a>
<li><a href="#fax">Sending mail to a FAX machine</a>
</ul>
<a name="compiling_installing"><h3>Compiling and installing Postfix</h3>
<ul>
<li><a href="#bind">Undefined symbols: ___dn_expand, ___res_init etc.</a>
<li><a href="#dbm_dirfno">Undefined symbols: dbm_pagfno, dbm_dirfno etc.</a>
<li><a href="#db">Using DB libraries on Solaris etc.</a>
</ul>
<hr>
<a name="stand_alone"><h3>Stand-alone machine</h3>
Out of the box, Postfix should work without change on a stand-alone
machine that is has direct Internet access. At least, that is how
Postfix installs when you download the Postfix source code. If you
are on a firewalled intranet, or if your machine is dial-up connected
only a small part of the time, see the respective sections.
<hr>
<a name="workstation_server"><h3>Workstations and servers</h3>
This section describes a workstation-server environment. All systems
send mail as user@domain. All systems receive mail for user@hostname.
The server receives mail for user@domain, too.
<p>
Postfix has sane defaults for all parameters, so the text shows
only the overrides. In particular, Postfix will relay mail only
for clients in its own domain (and subdomains) and in its class A,
B or C networks. The master.cf file (somewhat like inetd.conf)
needs tweaking only if you have a very slow or a very fast net/machine.
<p>
Workstation:
<pre>
<b>/etc/postfix/main.cf</b>:
myorigin = $mydomain
</pre>
<p>
Server:
<pre>
<b>/etc/postfix/main.cf</b>:
myorigin = $mydomain
mydestination = $myhostname, localhost.$mydomain, $mydomain
</pre>
<p>
In an environment like this. either the mail spool directory is
shared via NFS, users access their mailboxes via POP, or each user
receives her mail on her own workstation. In the latter case, each
user has an alias on the server that forwards mail to the respective
workstation:
<p>
Server:
<pre>
<b>/etc/aliases</b>:
joe: joe@joes.workstation
jane: jane@janes.workstation
</pre>
<p>
On some systems the alias database is not in <b>/etc/aliases</b>.
To find out the location for your system, execute the command
<b>postconf alias_maps</b>.
<hr>
<a name="null_client"><h3>Null clients</h3>
A null client is a machine that can only send mail. It receives no
mail from the network, and it does not deliver any mail locally. A
null client typically uses POP or NFS for mailbox access.
<p>
In the following example, mail is sent as user@domain, and all mail
is forwarded to the mail server that is responsible for the local
domain.
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
myorigin = $mydomain
relayhost = $mydomain
<b>/etc/postfix/master.cf</b>:
Comment out the SMTP server entry
Comment out the local delivery agent entry
</pre>
<p>
Since everything sends mail as user@domain, nothing sends mail as
user@nullclient, and therefore no special configuration needs to
be done on the mail server for mail addressed to user@nullclient.
<hr>
<a name="intranet"> <h3>Running Postfix inside an intranet</h3> </a>
The simplest way to set up Postfix on a host inside a firewalled
network is to send all your mail to an intranet mail gateway, and
to let that mail gateway take care of forwarding.
<p>
<ul>
<li>Send mail as user@domain. This is optional but highly recommended
because it allows users to change machines without hassle.
<pre>
<b>/etc/postfix/main.cf</b>:
myorigin = $mydomain
</pre>
<p>
<li>Forward <i>all</i> mail to an intranet mail gateway, except
for mail for the local machine:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
relayhost = $mydomain
</pre>
<p>
This assumes that your organization has set up internal MX records
for the local domain.
<p>
If your intranet does not use MX records internally, you have to
specify the intranet mail gateway host itself:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
relayhost = host.my.domain
</pre>
<p>
If your intranet does not use DNS internally, you have to disable
DNS lookups as well:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
disable_dns_lookups = yes
</pre>
<p>
<li>In addition to the above you can configure Postfix to deliver
intranet mail directly instead of sending it via the intranet
mail gateway.
<p>
Specify routing information for the internal domain in the <a
href="transport.5.html">transport</a> table, and enable <a
href="transport.5.html">transport</a> table lookups.
<p>
<pre>
<b>/etc/postfix/transport</b>:
my.domain smtp:
.my.domain smtp:
thishost.my.domain local: <blink>!important!</blink>
localhost.my.domain local: <blink>!important!</blink>
<b>/etc/postfix/main.cf</b>:
transport_maps = hash:/etc/postfix/transport
</pre>
<p>
Important: do not omit the entries that deliver mail locally, or
else mail will bounce with a "mail loops to myself" condition.
<p>
Specify <b>dbm:/etc/postfix/transport</b> if your system
uses <b>dbm</b> files instead of <b>db</b>.
<p>
Execute the command <b>postmap /etc/postfix/transport</b> whenever
you edit the transport table.
<p>
<li>Execute the command <b>postfix reload</b> to make the
changes effective.
</ul>
<hr>
<a name="firewall"><h3>Running Postfix on a firewall</h3> </a>
Note: this text applies to Postfix versions dated 19991115
and later only. To find out what Postfix version you have,
execute the command <b>postconf mail_version</b>.
<p>
How to set up Postfix on the firewall machine so that it relays
mail for <i>my.domain</i> to a gateway machine on the inside, and
so that it refuses mail for <i>*.my.domain</i>? The problem is that
the standard <a href="uce.html#relay_domains">relay_domains</a>
mail relaying restriction allows mail to <i>*.my.domain</i> when
you specify <i>my.domain</i>.
<p>
<ul>
<li>Specify a null <a href="uce.html#relay_domains">relay_domains</a>
parameter plus a <a href="transport.5.html">transport</a> table to
route mail for <i>my.domain</i> to the inside machine:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
mydestination = $myhostname, my.domain, localhost.my.domain
relay_domains =
transport_maps = hash:/etc/postfix/transport
<b>/etc/postfix/transport</b>:
my.domain smtp:inside-gateway.my.domain (forwards user@domain)
.my.domain smtp:inside-gateway.my.domain (forwards user@firewall)
<b>/etc/postfix/master.cf</b>:
Comment out the local delivery agent
</pre>
<p>
Specify <b>dbm:/etc/postfix/transport</b> if your system uses <b>dbm</b>
files instead of <b>db</b>.
<p>
<li>Execute the command <b>postmap /etc/postfix/transport</b>
whenever you change the transport table.
<p>
<li>Execute the command <b>postfix reload</b> after a
configuration change.
</ul>
<hr>
<a name="dialup"><h3>Running Postfix on a dialup machine</h3></a>
This section applies to dialup connections that are down most of
the time. For dialup connections that are up 24x7, see the <a
href="#workstation_server">workstations and servers</a> section
instead.
<p>
If you do not have your own hostname (as with dynamic IP addressing)
and must send mail as user@your-isp.com, you should also study the
the section on <a href="#some_local">delivering some users locally
while sending mail as user@domain</a>.
<ul>
<li> Route all outgoing mail to your provider.
<p>
If your machine is disconnected most of the time, there isn't
a lot of opportunity for Postfix to deliver mail to hard-to-reach
corners of the Internet. It's better to drop the mail to a machine
that is connected all the time.
<p>
<pre>
<b>/etc/postfix/main.cf:</b>
relayhost = smtprelay.someprovider.com
</pre>
<p>
<li> <a name="spontaneous_smtp">Disable spontaneous SMTP mail
delivery (on-demand dialup IP only).</a>
<p>
Normally, Postfix attempts to deliver outbound mail at its convenience.
If your machine uses on-demand dialup IP, this causes your system
to place a telephone call whenever you submit new mail, and whenever
Postfix retries to deliver delayed mail. To prevent such telephone
calls from being placed, disable spontaneous SMTP mail deliveries.
<p>
<pre>
<b>/etc/postfix/main.cf:</b>
defer_transports = smtp (Only for systems that use on-demand dialup IP)
</pre>
<p>
<li> Disable SMTP client DNS lookups (dialup LAN only).
<p>
Some people use Postfix to deliver mail across a LAN that is
disconnected most of the time. Under such conditions, mail delivery
can suffer from delays while the Postfix SMTP client performs sender
and recipient domain DNS lookups in order to be standards-compliant.
To prevent these delays, disable all SMTP client DNS lookups.
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
disable_dns_lookups = yes (Only for delivery across LANs that are disconnected most of the time)
</pre>
<p>
<i> When you disable DNS lookups, you must specify the</i>
<b>relayhost</b> <i> as either a numeric IP address, or as a hostname
that resolves to one or more IP addresses (with DNS lookup disabled,
Postfix does no MX lookup</i>).
<p>
<li> Flush the mail queue whenever the Internet link is established.
<p>
Put the following command into your PPP or SLIP dialup scripts:
<p>
<dl>
<dd><b>/usr/sbin/sendmail -q</b> (whenever the Internet link is up)
</dl>
<p>
The exact location of the <b>sendmail</b> command is system-specific.
With some UNIX versions, use <b>/usr/lib/sendmail</b>.
<p>
In order to find out if the mail queue is flushed, use something
like:
<p>
<pre>
#!/bin/sh
# Start deliveries.
/usr/sbin/sendmail -q
# Allow deliveries to start.
sleep 10
# Loop until all messages have been tried at least once.
while mailq | grep '^[^ ]*\*' >/dev/null
do
sleep 10
done
</pre>
<p>
If you have disabled <a href="#spontaneous_smtp">spontaneous SMTP
mail delivery</a>, you also need to run the above command every
now and then while the dialup link is up, so that newly-posted mail
is flushed from the queue.
</ul>
<hr>
<a name="verbose"><h3>Postfix breaks "sendmail -v"</h3> </a>
Some people will complain that <b>sendmail -v</b> no longer shows
the actual mail delivery.
<p>
With a distributed mail system such as Postfix, this is difficult
to implement. Unlike sendmail, no Postfix mail delivery process
runs under control by a user. Instead, Postfix delivers mail with
daemon processes that have no parent-child relationship with user
processes. This eliminates a large variety of potential security
exploits with environment variables, signal handlers, and with
other process attributes that UNIX passes on from parent process
to child process.
<p>
Postfix uses multiple processes in order to insulate subsystems
from each other. Making the delivery agents talk directly to user
processes would defeat a lot of the effort that went into making
Postfix more secure than ordinary mailers.
<hr>
<a name="delayed"><h3>Postfix sends no "delayed mail" notices</h3>
<blockquote>
When I was using Sendmail, after 4 hours, it would always send a receipt
back to the sender saying mail delivery is delayed.
</blockquote>
<p>
In order to make Postfix send "delayed mail" notifications after
four hours, specify:
<p>
<pre>
<b>/etc/postfix/main.cf</b>
delay_warning_time = 4
</pre>
<p>
With Postfix, delayed mail notices are turned off by default -
people get enough mail already.
<hr>
<a name="duplicate"><h3>Postfix sends duplicate mail</h3> </a>
Some people will complain that Postfix sends duplicate messages.
This happens whenever one message is mailed to multiple addresses
that reach the same user. Examples of such scenarios are:
<p>
<ul>
<li>One message is sent to the user, and to an alias that lists
the user. The user receives one copy of the mail directly, and
one copy via the alias.
<p>
<li>One message is sent to multiple aliases that list the user.
The user receives one copy of the mail via each alias.
</ul>
<p>
Some people will even argue that this is the "right" behavior. It
is probably more a matter of expectation and of what one is used to.
<p>
This can be "fixed" only by making Postfix slower. In the above
examples, Postfix would first have to completely expand all
distribution lists before starting any delivery. By design, Postfix
delivers mail to different destinations in parallel, and local
delivery is no exception. This is why Postfix can be faster than
sendmail.
<hr>
<a name="metoo"><h3>Postfix sends mail to every member of a
distribution list</h3> </a>
Some people will complain that Postfix sends mail to every member
of a distribution list, including the poster. By default, Sendmail
deletes the poster from distribution lists. Sendmail sends mail to
the poster only when the "metoo" flag is explicitly turned on.
<p>
Wietse believes that Postfix implements the "right" behavior,
and suspects that Sendmail's default behavior is a remnant from a
dark past when Sendmail used a pretty crummy algorithm to avoid
aliasing loops.
<hr>
<a name="open_relay"><h3>Help! Postfix is an open relay</h3>
According to some relay checking software, Postfix accepts
mail for arbitrary non-local destinations:
<p>
<pre>
>>> MAIL FROM:<someone@some.where>
<<< 250 Ok
>>> RCPT TO:<test@some.other.site@some.site>
<<< 250 Ok
>>> DATA
<<< 354 End data with <CR><LF>.<CR><LF>
>>> (message body)
<<< 250 Ok: queued as A958F5A15
</pre>
<p>
Don't Panic! Upgrade to a Postfix version of 19991227 or later.
<p>
With earlier Postfix versions,
<ol>
<li>Good but confusing: a Postfix primary MX host for <i>some.site</i>
accepts <i>test@some.other.site@some.site</i> then bounces it because
<i>test@some.other.site</i> is not a known local username.
<li>Good: a Postfix primary MX host for <i>some.site</i> rejects
other source-routed addresses such as <i>test%some.other.site@some.site</i>
or <i>some.other.site!test@some.site</i>.
<li>Loophole: a Postfix backup MX host for <i>some.site</i> forwards
source-routed addresses such as <i>test@some.other.site@some.site</i>
or <i>test%some.other.site@some.site</i> to a primary MX host for
<i>some.site</i>. Depending on the primary MX host's mailer
configuration, the primary MX host could then spam the mail into
the Internet.
</ol>
<p>
With newer Postfix versions,
<ol>
<li>A Postfix primary MX host for <i>some.site</i> host rejects
<i>test@some.other.site@some.site</i> just like it rejects
<i>test%some.other.site@some.site</i>. This ends the confusion
mentioned in 1 above.
<li>A Postfix backup MX host for <i>some.site</i> host rejects
source-routed addresses including <i>test@some.other.site@some.site</i>.
This closes the loophole mentioned in 3 above.
</ol>
<p>
To be precise, Postfix UCE restrictions refuse to forward source-routed
addresses under the following conditions:
<p>
<ul>
<li> <a href="uce.html#check_relay_domains">check_relay_domains</a>:
reject when the destination is not local and when the client hostname
does not match <a href="uce.html#relay_domains">relay_domains</a>.
<li> <a
href="uce.html#permit_auth_destination">permit_auth_destination</a>:
skip when the destination is not local.
<li> <a
href="uce.html#reject_unauth_destination">reject_unauth_destination</a>:
reject when the destination is not local.
<li> <a href="uce.html#permit_mx_backup">permit_mx_backup</a>:
reject when the destination is not local.
<li> Other UCE restrictions (e.g., SMTPD access maps) are not aware
of sender-provided routing information.
</ul>
<p>
However, a Postfix primary MX host for still forwards source-routed
addresses <b>if received from a trusted client</b>, just like it
did before.
<p>
In order to have guaranteed protection against source-routed relaying
through trusted SMTP clients, specify a regular expression restriction
ahead of the other SMTPD recipient restrictions:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
smtpd_recipient_restrictions =
regexp:/etc/postfix/regexp_access
<i>...other restrictions...</i>
<b>/etc/postfix/regexp_access</b>:
/[%!@].*[%!@]/ 550 Sender specified routing is not supported here.
</pre>
<p>
This would be installed on all MX hosts.
<hr>
<a name="mobile"><h3>Relaying mail for mobile users </h3>
<blockquote>
I have Postfix setup on a machine but I'd like to have a select
group of Internet users be able to relay mail through it. I'd
either like to base the relaying on IP address (e.g., a 256-block
for dynamic IP people) or on hostname (whatever.dialup.isp.com)
</blockquote>
<p>
The most preferable way is to have users submit mail via some
authenticated protocol instead of plain old SMTP.
<p>
The next best way is to use plain old SMTP and to authenticate the
user first, for example, with a "please login via POP before using
SMTP" scheme. In that case, some non-Postfix software such as <a
href="http://www.mbnet.mb.ca/howto/dynamic.htm">DRAC</a> maintains
a Postfix-compatible access table with client IP address information:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
smtpd_recipient_restrictions =
permit_mynetworks
check_client_access hash:/etc/postfix/client_access
check_relay_domains
<b>/etc/postfix/client_access</b>:
4.3.2.1 OK
5.4.3.2 987654321
</pre>
<p>
Specify <B>dbm</b> instead of <b>hash</b> if your system uses
<b>dbm</b> files instead of <b>db</b> files.
<p>
A less preferable way is based on client IP address (for example,
a 256-block) or DNS hostname (for example, whatever.pop.isp.com).
This scheme does not authenticate the user. If you use IP/DNS-based
relay access control, pray that no customer with that same ISP
points their spam software at your machine, or else you may end up
on internet-wide black lists.
<p>
The least preferable way is based on the sender address. It is
trivially easy to spoof by anyone who ever received mail from your
site. If you use sender address access control, pray that no
spammer ever finds out the address of your users.
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
smtpd_recipient_restrictions =
permit_mynetworks
check_client_access hash:/etc/postfix/client_access
check_sender_access hash:/etc/postfix/sender_access
check_relay_domains
<b>/etc/postfix/client_access</b>:
11.22.33 OK
dialup.isp.com OK
<b>/etc/postfix/sender_access</b>:
joe@my.domain OK
blow@my.domain OK
</pre>
<hr>
<a name="relay_restrict"><h3>Restricting what users can send mail to off-site destinations</h3>
<blockquote>
How can I configure Postfix in a way that some users can send mail
to the internet and other users not. The users with no access should
receive a generic bounce message. Please don't discuss whether such
access restrictions are necessary, it was not my decision.
</blockquote>
<p>
Postfix has support for per-user restrictions. The restrictions
are implemented by the SMTP server. Thus, users that violate the
policy have their mail rejected by the SMTP server. Like this:
<p>
<blockquote>
<pre>
550 <user@remote>: Access denied
</pre>
</blockquote>
<p>
The implementation uses two lookup tables. One table defines what
users are restricted in where they can send mail, and the other
table defines what destinations are local. It is left as an exercise
for the reader to change this into a scheme where only some users
have permission to send send mail to off-site destinations, and
where most users are restricted.
<p>
The example assumes DB/DBM files, but this could also be done with
LDAP or SQL.
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
smtpd_recipient_restrictions =
hash:/etc/postfix/restricted_senders
...other stuff...
restriction_classes = local_only
local_only = check_recipient_access hash:/etc/postfix/local_domains, reject
<b>/etc/postfix/restricted_senders</b>:
foo@domain local_only
bar@domain local_only
<b>/etc/postfix/local_domains</b>:
this.domain OK (matches this.domain and subdomains)
that.domain OK (matches that.domain and subdomains)
</pre>
<p>
Specify <B>dbm</b> instead of <b>hash</b> if your system uses
<b>dbm</b> files instead of <b>db</b> files.
<p>
The <b>restriction_classes</b> verbiage exists so that Postfix can
open <b>/etc/postfix/local_domains.db</b> before entering a chroot
jail, so it is only an artefact of implementation.
<p>
This scheme does not authenticate the user, therefore it can be
bypassed in several ways:
<p>
<ul>
<li>By sending mail as someone else who does have permission to
send mail to off-site destinations.
<p>
<li>By sending mail as yourself via a less restrictive mail relay
host.
</ul>
<hr>
<a name="timeouts"><h3>Mail fails consistently with timeout or lost connection</h3></a>
Every now and then, mail fails with "timed out while sending end
of data -- message may be sent more than once", or with: "lost
connection after DATA". Network outages happen, systems crash.
There isn't much you can do about it. Usually the problem goes away
by itself.
<p>
However, when you see mail deliveries fail consistently, you may
have a different problem: broken path MTU discovery.
<p>
A little background is in order. With the SMTP protocol, the HELO,
MAIL FROM and RCPT TO commands and responses are relatively short.
When you're talking to sendmail, every command and every response
is sent as a separate packet, because sendmail cannot implement
ESMTP command pipelining.
<p>
The message content, however, is sent as a few datagrams, each
datagram typically a kbyte large or even bigger, depending on your
local network MTU.
<p>
When mail fails consistently due to a timeout, I suspect that the
sending machine runs a modern UNIX which implements path MTU
discovery. That causes the machine to send packets as large as it
would send over the LAN, with the IP DON'T FRAGMENT bit set,
preventing intermediate routers from fragmenting the packets that
are too big for their networks.
<p>
Depending on what network path a message follows, some router on
the way responds with an ICMP MUST FRAGMENT message saying the
packet is too big. Normally, the sending machine will re-send the
data after chopping it up into smaller pieces.
<p>
However, things break when some router closer to the sending system
is dropping such ICMP feedback messages, in a mistaken attempt to
protect systems against certain attacks. In that case, the ICMP
feedback message never reaches the sending machine, and the connection
times out.
<p>
This is the same configuration problem that causes trouble with
web servers behind a misconfigured packet filter: small images/files
are sent intact, large images/files time out because the server
does not see the MUST FRAGMENT ICMP feedback messages.
<p>
Workaround: disable path MTU discovery at the sending machine. Mail
will get out, but of course everyone else will still suffer. How
to disable path MTU discovery? It depends. Solaris has an <b>ndd</b>
command; other systems use different means such as <b>sysctl</b>
to control kernel parameters on a running system.
<p>
Fix: find the router that drops the ICMP MUST FRAGMENT messages,
and convince the person responsible for it to fix the configuration.
<hr>
<a name="root"> <h3>Root's mail is delivered to nobody</h3>
If you use <a href="#procmail">procmail</a> (or some other command)
for local mail delivery, Postfix will not deliver mail as root.
Instead, Postfix runs <b>procmail</b> (or whatever) as <b>nobody</b>.
Perhaps some day Wietse will trust Postfix enough to run external
commands as <b>root</b>.
<p>
Solution: just like you're not supposed to log in as <b>root</b>
(except for unusual conditions), you're not supposed to receive
mail as <b>root</b>.
<p>
<ul>
<li>Create a mail alias for <b>root</b> that forwards mail to a
real user.
<p>
<pre>
<b>/etc/aliases:</b>
root: you
</pre>
<p>
<li>Execute the command <b>newaliases</b> whenever you change the
alias database.
</ul>
<p>
On some systems the alias database is not in <b>/etc/aliases</b>.
To find out the location for your system, execute the command
<b>postconf alias_maps</b>.
<hr>
<a name="bogus"><h3>Postfix accepts mail for non-existing local users</h3>
The information in this section applies to Postfix versions 19991216
and later. See elsewhere for <a href="#virtual_setup">unknown
virtual</a> users.
<p>
By default, the Postfix SMTP server does not know what local users
exist, and will happily accept mail for <i>unknown@your.site</i>.
The reason is that different local delivery agents have different
types of user databases.
<p>
Of course mail for a non-existent local user will eventually bounce
as undeliverable, but why accept such mail in the first place? You
can tell the Postfix SMTP server how to find out if a user exists by
listing all tables with local addresses in the <b>local_recipient_maps</b>
parameter:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
local_recipient_maps = $alias_maps, unix:passwd.byname
</pre>
<p>
The above should work on UNIX systems, provided that you use the
Postfix local delivery agent. However, if you run the Postfix SMTP
server chrooted, on some systems it will be necessary to have a
copy of the passwd file inside the chroot jail (typically: in
<b>/var/spool/postfix/etc</b>).
<p>
By default, the Postfix SMTP server does know about Postfix <a
href="virtual.5.html">virtual</a> maps, and will reject mail for
<i>unknown@virtual.domain</i> without further configuration.
<hr>
<a name="some_local"><h3>Delivering some users locally while sending
mail as user@domain</h3></a>
<ul>
<li>In order to send mail as <i>user@domain.name</i>, specify what
domain is to be appended to addresses that do not have a domain:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
myorigin = domain.name
</pre>
<p>
<li>In order to receive some users locally, such as <b>root</b> or
<b>postmaster</b>, specify a virtual lookup table with the non-default
destinations:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
virtual_maps = hash:/etc/postfix/virtual
<b>/etc/postfix/virtual</b>:
root root@localhost
postmaster postmaster@localhost
</pre>
<p>
Specify <B>dbm</b> instead of <b>hash</b> if your system uses
<b>dbm</b> files instead of <b>db</b> files.
<p>
<li>Execute the command <b>postmap /etc/postfix/virtual</b> whenever
you edit the the <b>virtual</b> table.
<p>
<li>Execute the command <b>postfix reload</b> to make the changes
effective.
</ul>
<hr>
<a name="maildir"><h3>Support for maildir-style mailboxes</h3> </a>
<b>Maildir</b> is a specific one-file-per-message organization that
was introduced with the <b>qmail</b> system by Daniel Bernstein.
In order to turn on <b>maildir</b>-style delivery, specify,
for example:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
home_mailbox = Maildir/
</pre>
<p>
Any relative pathname that ends in <b>/</b> turns on <b>maildir</b>
delivery. The <b>home_mailbox</b> value is appended to the user's
home directory pathname.
<p>
The <b>maildir</b> format is also supported with delivery via
aliases or via <b>.forward</b> files. Specify <i>/file/name/</i>
as destination. The trailing <b>/</b> turns on <b>maildir</b>
delivery.
<hr>
<a name="procmail"><h3>Using Procmail for system-wide local delivery</h3> </a>
Warning: if you use <b>procmail</b> in this manner, you must set
up an alias for <b>root</b> that forwards mail for <b>root</b> to
a real user. See the FAQ entry titled "<a href="#root">Mail for root
is delivered to nobody</a>".
<ul>
<li>Specify that all mailbox delivery is to be done by <b>procmail</b>.
For example:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
mailbox_command = /path/to/procmail
<b>/etc/postfix/main.cf</b>:
mailbox_command = /path/to/procmail -a $EXTENSION
</pre>
<p>
If you can, avoid using any shell meta characters or built-ins such
as <b>$</b> or <b>"</b> or <b>IFS</b> or <b>&&</b>, because
they force Postfix to run an expensive shell process. However,
procmail is a pig, and the gain of avoiding a shell can be
unnoticeable.
<p>
<li>Execute the command <b>postfix reload</b> to make the changes
effective.
</ul>
Postfix exports information via environment variables. The contents
are censored. Characters that may have special meaning to the shell,
including whitespace, are replaced by underscores.
<p>
<blockquote>
<dl>
<dt><b>DOMAIN</b> <dd> The text to the right-hand side of the
<b>@</b> in the recipient address.
<dt><b>EXTENSION</b> <dd> Optional address extension part.
<dt><b>HOME</b> <dd> The recipient's home directory.
<dt><b>LOCAL</b> <dd> The text to the left-hand side of the <b>@</b>
in the recipient address, for example, <b>$USER+$EXTENSION</b>.
<dt><b>LOGNAME</b> <dd> The recipient username.
<dt><b>RECIPIENT</b> <dd> The entire recipient address,
<b>$LOCAL@$DOMAIN</b>.
<dt><b>SHELL</b> <dd> The recipient's login shell.
<dt><b>USER</b> <dd> The recipient username.
</dl>
</blockquote>
<hr>
<a name="delivered"><h3>Getting rid of the ugly Delivered-To: header</h3> </a>
Some people will complain about the ugly <b>Delivered-To:</b>
message header that Postfix prepends to their mail. By default,
Postfix prepends this header when forwarding mail, and when delivering
to file (mailbox) or command. The purpose is to stop mail forwarding
loops as early as possible, that is, before they have a chance to
happen. But the header is ugly, no question about it.
<p>
Solutions, ranging from fighting symptoms to turning off the
<b>Delivered-To:</b> header:
<p>
<ul>
<li>
Fortunately, many mail user agents have per-user or even system-wide
configuration files that can be set up to suppress <b>Delivered-To:</b>
headers (for example <b>~/.mailrc</b> and <b>/usr/lib/Mail.rc</b>).
<p>
<li>
With mailing lists, <b>Delivered-To:</b> can get in the way when
the list exploder uses a "secret" alias that should not be shown
in outbound mail. The recommended solution is to use a regular
expression-based filter at the SMTP port:
<p>
<dl>
<dt><b>/etc/postfix/main.cf:</b>
<dl>
<dt><tt>smtpd_recipient_restrictions = ... regexp:/etc/postfix/access_regexp ...</tt>
<dt><tt>smtpd_recipient_restrictions = ... pcre:/etc/postfix/access_regexp ...</tt>
</dl>
<p>
<dt><b>/etc/postfix/access_regexp:</b>
<dl>
<dt><tt>/^(.*)-outgoing@(.*)/ 554 Use $1@$2 instead</tt>
</dl>
</dl>
<p>
POSIX regular expression support (regexp) is enabled by default on
modern UNIX systems. Perl-compatible regular expression support
(pcre) is optional; see the PCRE_README file in the top-level
Postfix source directory.
<p>
<li>
The <b>prepend_delivered_header</b> configuration parameter controls
when <b>Delivered-To:</b> is prepended. The default setting is
<b>command, file, forward</b> (translation: prepend <b>Delivered-To:</b>
when delivering to command, when delivering to file, and when
forwarding mail). <i>Turning off <b>Delivered-To:</b> when forwarding
mail is not recommended</i>.
</ul>
<p>
See also the FAQ item for problems with the <b>majordomo</b> <a
href="#majordomo-approve">approve</a> command.
<hr>
<a name="majordomo-approve"><h3>Postfix breaks the majordomo "approve"
command</h3> </a>
The Postfix local delivery agent prepends a <b>Delivered-To:</b>
message header to prevent mail forwarding loops. With <b>majordomo</b>
mailing lists, <b>Delivered-To:</b> gets in the way when the
moderator wants to approve postings that were sent to the list.
The Postfix system claims that the mail is looping.
<p>
Currently, the recommended workaround is to edit the <b>approve</b>
script to strip any header lines that match:
<p>
<dl>
<dd><b>/delivered-to/i</b>
</dl>
<p>
Yes, this assumes that the moderator knows what she is doing.
<p>
A less-preferred workaround is to not insert <b>Delivered-To:</b>
when delivering to commands such as majordomo. See the FAQ entry
titled "<a href="#delivered">Getting rid of the ugly Delivered-To:
header</a>".
<hr>
<a name="worm"><h3>Postfix accepts MAIL FROM and RCPT TO "|command"</h3>
With Postfix, | or / has special meaning only when it appears in
aliases, .forward files or in :include: files. It has no special
meaning in mail addresses.
<p>
If you must receive mail for systems with 10-year old vulnerabilities,
it is prudent to set up a regexp filter that rejects potentially
harmful MAIL FROM or RCPT TO commands.
<p>
<pre>
/etc/postfix/main.cf:
smtpd_sender_restrictions =
regexp:/etc/postfix/envelope-regexp
reject_unknown_sender_domain
smtpd_recipient_restrictions =
regexp:/etc/postfix/envelope-regexp
permit_mynetworks
check_relay_domains
/etc/postfix/envelope-regexp:
/[/|]/ REJECT
</pre>
<p>
However, rejecting all envelope addresses with / causes trouble
with simple-minded X.400 to Internet address mappings that leave
the X.400 address structure exposed.
<p>
See also the documentation on <a href="uce.html#header_checks">header
checks</a> restrictions for message header contents. These restrictions
can be used to protect against attacks with command/file destinations
in, for example, Errors-To: or Return-Receipt_To: message headers.
<hr>
<a name="internal-list"><h3>Protecting internal email distribution lists</h3>
<blockquote>
We want to implement an internal email distribution list. Something
like all@our.domain.com, which aliases to all employees. My first
thought was to use the aliases map, but that would lead to "all"
being accessible from the "outside", and this is not desired...
:-)
</blockquote>
Postfix can implement per-address access controls. What follows
is based on the SMTP client IP address, and therefore is subject
to IP spoofing.
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
smtpd_recipient_restrictions =
hash:/etc/postfix/access
..the usual stuff...
<b>/etc/postfix/access</b>:
all permit_mynetworks,reject
</pre>
<p>
Specify <B>dbm</b> instead of <b>hash</b> if your system uses
<b>dbm</b> files instead of <b>db</b> files.
<p>
Now, that would be sufficient when your machine receives all Internet
mail directly from the Internet. That's unlikely if your network
is a bit larger than an office. For example your backup MX hosts
would "launder" the client IP address of mail from outside so it
would appear to come from a trusted machine.
<p>
In the general case you need two lookup tables: one table that
lists destinations that need to be protected, and one table that
lists domains that are allowed to send to the protected destinations.
<p>
What follows is based on the sender SMTP envelope address, and
therefore is subject to SMTP sender spoofing.
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
smtpd_recipient_restrictions =
hash:/etc/postfix/protected_destinations
..the usual stuff...
smtpd_restriction_classes = insiders_only
insiders_only = check_sender_access hash:/etc/postfix/insiders, reject
<b>/etc/postfix/protected_destinations</b>:
all@my.domain insiders_only
all@my.hostname insiders_only
<b>/etc/postfix/insiders</b>:
my.domain OK
another.domain OK
</pre>
<p>
The smtpd_restriction_classes verbiage is needed so that Postfix
knows what lookup tables to open before it goes to chroot jail.
It is only an artefact of the implementation.
<p>
Getting past this scheme is relatively easy, because all one has
to do is to spoof the SMTP sender address.
<p>
If the internal list is a low-volume one, perhaps it makes more
sense to make it moderated.
<hr>
<a name="virtual_setup"><h3>How to configure a Postfix virtual domain</h3>
Problem:
<p>
<ul>
<li>Postfix does not refuse mail for unknown virtual users.
<li>Mail for unknown virtual users fails with "mail loops back to
myself".
<li>Postfix refuses mail for virtual domains with "user unknown".
<li>Postfix refuses mail for virtual domains with "relay access
denied".
</ul>
<p>
Solution:
<p>
<ul>
<li> Add a magical entry to the Postfix virtual maps for
each Postfix virtual domain:
<p>
<pre>
<b>/etc/postfix/virtual</b>:
virtual.domain whatever
</pre>
<p>
<li> Do not list Postfix virtual domains in the <a
href="basic.html#mydestination">mydestination</a> parameter.
<li> Do not list Postfix virtual maps in the <b>local_recipient_maps</b>
parameter.
<li>As of Postfix version 19991226 it is no longer necessary to
specify virtual maps in the <a
href="uce.html#relay_domains">relay_domains</a> parameter.
</ul>
<p>
For more information on how to set up virtual domains, see the <a
href="virtual.5.html">virtual</a> manual page.
<hr>
<a name="command"><h3>Commands don't work in Postfix virtual maps</h3>
Delivering mail to a command is a security-sensitive operation,
because the command must be executed with the right privileges.
Only <b>root</b>-privileged software such as the Postfix local
delivery agent can set the privileges for a command.
<p>
For security reasons, Postfix tries to avoid using <b>root</b>
privileges where possible. In particular, Postfix virtual mapping
is done by an unprivileged daemon, so there is no secure way to
execute commands found in virtual maps.
<p>
Solution: specify a local alias instead. The Postfix local delivery
agent has sufficient privilege to execute commands with the right
privileges.
<p>
<ul>
<li>Set up a local alias that executes the command:
<p>
<pre>
<b>/etc/aliases</b>:
name-virtual.domain "|/some/where/command..."
</pre>
<p>
<li>Execute the command <b>newaliases</b> whenever you edit the
alias database.
<p>
<li>Forward mail for the virtual address to the local alias:
<p>
<pre>
<b>/etc/postfix/virtual</b>:
virtual.domain whatever
name@virtual.domain name-virtual.domain
</pre>
<p>
<li>Execute the command <b>postmap /etc/postfix/virtual</b> whenever
you edit the virtual database.
</ul>
<p>
Note: on some systems the alias database is not in <b>/etc/aliases</b>.
To find out the location for your system, execute the command
<b>postconf alias_maps</b>.
<hr>
<a name="domain_mailbox"><h3>Receiving a virtual domain in a mailbox</h3>
Question: how to receive all mail for a domain in a mailbox without
losing the original recipient information? The Postfix Delivered-To:
mail header shows only the mailbox owner, not the virtual address
that the mail was sent to.
<p>
Answer: I hope we all agree that delivering a domain to a mailbox
is disgusting practice. Forwarding mail via SMTP or UUCP would be
a much better choice. Unfortunately, neither SMTP nor UUCP are a
usable alternative for legions of windows users.
<p>
That said, it is possible to propagate the original virtual recipient
information to the Delivered-To: header. The trick is to use a
virtual map that uses regular expressions instead of the more
traditional indexed files.
<p>
The following delivers <i>username@virtual.domain</i> with a
Delivered-To: message header that contains <i>joe+username@your.domain</i>.
Postfix already puts the envelope sender address in the Return-Path:
header. The information in the Delivered-To: and Return-Path:
headers is sufficient to reliably implement a domain in a mailbox.
<p>
<pre>
<b>/etc/postfix/main.cf</b>
recipient_delimiter = +
virtual_maps =
<i>...non-regexp virtual maps...</i>
regexp:/etc/postfix/virtual_regexp
<b>/etc/postfix/virtual_regexp</b>
/^virtual\.domain$/ whatever
/^(.*\)@virtual\.domain$/ joe+$1
</pre>
<p>
Notes:
<ul>
<li> Be sure to specify the <b>^</b> and <b>\</b> and <b>$</b> or
else you may have false hits.
<li> Maps with regular expressions are searched sequentially. This
can be expensive when you list many domains in regular expression
maps.
<li> Postfix has <b>regexp </b> map support only on modern UNIXes.
Instead of <b>regexp </b> maps your Postfix system may also support
<b>pcre</b> maps which have a similar syntax. To find out what maps
your system supports, use the command <b>postconf -m</b>.
</ul>
<hr>
<a name="masquerade"><h3>Address masquerading with exceptions</h3></a>
For people outside your organization it can be desirable to only
see addresses of the form <i>user@company.com</i> rather than
addresses with individual internal host names. This can be achieved
with address masquerading.
<p>
Address masquerading is intended for use only on mail gateways.
<ul>
<li>In order to have all mail through the gateway host appear as
coming from <i>user@my.domain</i>, specify:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
masquerade_domains = $mydomain
</pre>
<p>
Note that the gateway should have <b><a
href="rewrite.html#append_dot_mydomain">append_dot_mydomain</a></b>
and <b><a href="rewrite.html#append_at_myorigin">append_at_myorigin</a></b>
turned on (which is the default setting) so that all addresses are
fully qualified before they are subjected to address masquerading.
</ul>
<p>
In some cases, you may wish to have certain users or hosts exempted
from masquerading.
<ul>
<li>To exempt certain <i>users</i> from masquerading,
such as <b>root</b>, specify:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
masquerade_exceptions = root
</pre>
<p>
<li>To exempt certain <i>hosts</i> from masquerading, write
<b>masquerade_domains</b> as:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
masquerade_domains = somehost.my.domain otherhost.my.domain $mydomain
</pre>
<p>
Note that the order above is crucial: exemptions such as
<i>somehost.my.domain</i> must precede <i>$mydomain</i> in the
statement.
<p>
It should go without saying that if a particular host you wish to
exempt this way is originating mail as <i>user@my.domain</i> in
the first place, you can hardly exempt it.
<p>
</ul>
As usual, execute the command <b>postfix reload</b> to make the changes
effective.
<p>
<hr>
<a name="scanning"><h3>Support for virus scanning</h3> </a>
Would not it be great if operating systems and applications actually
worked the way they are supposed to, instead of being as fragile
as today's products? Well, we can solve only one problem at a time.
<p>
Currently, Postfix has no hooks to let other programs inspect every
message, so the scanning has to be done before mail enters Postfix
or while mail leaves Postfix, for example at mailbox delivery time.
<p>
Examples:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
mailbox_command = /some/program ...
</pre>
<p>
This example specifies a command that delivers all local mail to
mailbox. See the sample <b>main.cf</b> file for examples. In
<b>/etc/aliases</b>, you must specify an alias for <b>root</b> that
directs mail to a real person, otherwise mail sent to <b>root</b>
will not work as expected.
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
mailbox_transport = foo
</pre>
<p>
This example delegates local mailbox delivery to the transport
<i>foo</i> as configured in <b>/etc/postfix/master.cf</b>. If you
follow this route you will build something around the pipe mailer.
See examples in <b>master.cf</b>.
<hr>
<a name="internet-uucp"><h3>Setting up an Internet to UUCP gateway</h3> </a>
Here is how to set up a machine that sits on the Internet and that
delivers <i>some</i> but not all non-local mail via UUCP. See the
<a href="#uucp-only">UUCP-only</a> FAQ entry for setting a UUCP-only
host.
<p>
<ul>
<li>You need an <b>rmail</b> program that extracts the sender
address from mail that arrives via UUCP, and that feeds the mail
into the Postfix <b>sendmail</b> command. Most UNIX systems come
with an <b>rmail</b> utility. If you're in a pinch, try the one
bundled with the Postfix source code in the <b>auxiliary</b>
directory. Some day Postfix may have its own <b>rmail</b> command.
<p>
<li>Specify that mail for, let's say, <i>some.domain</i>, should
be delivered via UUCP, for example, to a host named <i>uucp-host</i>:
<p>
<pre>
<b>/etc/postfix/transport</b>:
some.domain uucp:uucp-host
.some.domain uucp:uucp-host
</pre>
<p>
See the <a href="transport.5.html">transport</a> manual page
for more details.
<p>
<li>Execute the command <b>postmap /etc/postfix/transport</b> whenever
you change the <b>transport</b> file.
<p>
<li>Enable <b>transport</b> table lookups:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
transport_maps = hash:/etc/postfix/transport
</pre>
<p>
Specify <B>dbm</b> instead of <b>hash</b> if your system uses
<b>dbm</b> files instead of <b>db</b> files.
<p>
<li>Define a mail transport for delivery via UUCP:
<pre>
<b>/etc/postfix/master.cf</b>:
uucp unix - n n - - pipe
flags=F user=uucp argv=uux -r -n -z -a$sender - $nexthop!rmail ($recipient)
</pre>
<p>
This runs the <b>uux</b> command, and substitutes the next-hop
hostname (<i>uucp-host</i>) and the recipients before executing
the command. The <b>uux</b> command is executed without assistance
from the shell, so there are no problems with shell meta characters.
<p>
<li>Add <i>some.domain</i> to the list of domains that your site
is willing to relay mail for.
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
relay_domains = some.domain $mydestination ...
</pre>
<p>
See the <a href="uce.html#relay_domains">relay_domains</a>
configuration parameter description for details.
<p>
<li>Execute the command <b>postfix reload</b> to make the
changes effective.
</ul>
<hr>
<a name="uucp-only"><h3>Using UUCP as the default transport</h3> </a>
Here is how to relay all your mail over a UUCP link. See the <a
href="#internet-uucp">Internet to UUCP</a> FAQ entry for setting
up a machine that gateways between UUCP and SMTP.
<p>
<ul>
<li>There is no need for a <b>transport</b> table.
<p>
<li> Specify that all remote mail must be sent via the <b>uucp</b>
mail transport to your UUCP gateway host, say, <i>uucp-gateway</i>:
<p>
<pre>
<b>/etc/postfix/main.cf</b>:
relayhost = uucp-gateway
default_transport = uucp
</pre>
<p>
<li>Define a message transport for mail delivery via UUCP:
<p>
<pre>
<b>/etc/postfix/master.cf</b>:
uucp unix - n n - - pipe
flags=F user=uucp argv=uux -r -n -z -a$sender - $nexthop!rmail ($recipient)
</pre>
<p>
This runs the <b>uux</b> command, and substitutes the next-hop
hostname (<i>uucp-gateway</i>, or whatever you specified) and the
recipients before executing the command. The <b>uux</b> command
is executed without assistance from the shell, so there are no
problems with shell meta characters.
<p>
<li>Execute the command <b>postfix reload</b> to make the
changes effective.
</ul>
<hr>
<a name="fax"><h3>Sending mail to a FAX machine</h3></a>
The following information is by Joerg Henne:
<p>
Over here we are using the scheme <fax number>@fax.our.domain with Postfix and
HylaFax. Here's the setup used:
<p>
<pre>
<b>/etc/postfix/master.cf</b>:
fax unix - n n - - pipe
flags= user=fax argv=/usr/bin/faxmail -d -n ${user}
<b>/etc/postfix/transport</b>:
fax.your.domain fax:localhost
<b>/etc/postfix/main.cf</b>:
transport_maps = hash:/etc/postfix/transport
</pre>
<p>
Specify <B>dbm</b> instead of <b>hash</b> if your system uses
<b>dbm</b> files instead of <b>db</b> files.
<p>
Note: be sure to not advertise <b>fax.your.domain</b> in the DNS...
<hr>
<a name="bind"><h3>Undefined symbols: ___dn_expand, ___res_init etc.</h3></a>
Question: When I build Postfix I get the following errors:
<p>
<pre>
ld: Undefined symbol
___dn_expand
___res_init
___res_search
*** Error code 1
</pre>
<p>
Answer: you're mixing BIND version 8 include files with a
different version of the resolver library.
<p>
Fix: use the right include files. For example:
<p>
<pre>
<tt>make makefiles CCARGS="-I/usr/include"</tt>.
</pre>
<hr>
<a name="dbm_dirfno"><h3>Undefined symbols: dbm_pagfno, dbm_dirfno etc.</h3></a>
Question: When I build Postfix I get the following errors:
<p>
<pre>
Undefined first referenced
symbol in file
dbm_pagfno ../lib/libutil.a(dict_dbm.o)
dbm_dirfno ../lib/libutil.a(dict_dbm.o)
</pre>
<p>
Answer: instead of using <b>/usr/include/ndbm.h</b>, you're building
Postfix with some incompatible third-party file, typically
<b>/usr/local/include/ndbm.h</b>.
<p>
Fix: get rid of the third-party ndbm.h include file.
<hr>
<a name="db"><h3>Using DB libraries on Solaris etc.</h3> </a>
The old <b>dbm</b> UNIX database has severe limitations when you
try to store lots of information. It breaks when the number of hash
collisions becomes so large that the entries no longer fit together
in a single disk block. The more modern <b>db</b> database does
not suffer these limitations. It is standard on 4.4BSD and Linux
systems.
<p>
In order to build Postfix with <b>db</b> support on UNIX systems
that do not have <b>db</b> support out of the box, you can use the
Berkeley DB source code from <a
href="http://www.sleepycat.com">www.sleepycat.com</a>. See the file
<b>DB_README</b> in the Postfix source code distribution for
instructions on how to build Postfix with Sleepycat's Berkeley DB.
<p>
One problem: older DB versions install a file
<b>/usr/local/include/ndbm.h</b> that is incompatible with
<b>/usr/include/ndbm.h</b>. Be sure to get rid of the bogus file.
See the FAQ entry titled "<a href="#dbm_dirfno">Undefined symbols:
dbm_pagfno, dbm_dirfno etc</a>".
<hr>
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