Postfix PostgreSQL Howto

Introduction

The Postfix pgsql map type allows you to hook up Postfix to a PostgreSQL database. This implementation allows for multiple pgsql databases: you can use one for a virtual(5) table, one for an access(5) table, and one for an aliases(5) table if you want. You can specify multiple servers for the same database, so that Postfix can switch to a good database server if one goes bad.

Busy mail servers using pgsql maps will generate lots of concurrent pgsql clients, so the pgsql server(s) should be run with this fact in mind. You can reduce the number of concurrent pgsql clients by using the Postfix proxymap(8) service.

Building Postfix with PostgreSQL support

These instructions assume that you build Postfix from source code as described in the INSTALL document. Some modification may be required if you build Postfix from a vendor-specific source package.

Note: to use pgsql with Debian GNU/Linux's Postfix, all you need to do is to install the postfix-pgsql package and you're done. There is no need to recompile Postfix.

In order to build Postfix with pgsql map support, you specify -DHAS_PGSQL, the directory with the PostgreSQL header files, and the location of the libpq library file.

For example: 

% make tidy
% make -f Makefile.init makefiles \
        "CCARGS=-DHAS_PGSQL -I/usr/local/include/pgsql" \
        "AUXLIBS_PGSQL=-L/usr/local/lib -lpq"

If your PostgreSQL shared library is in a directory that the RUN-TIME linker does not know about, add a "-Wl,-R,/path/to/directory" option after "-lpq".

Postfix versions before 3.0 use AUXLIBS instead of AUXLIBS_PGSQL. With Postfix 3.0 and later, the old AUXLIBS variable still supports building a statically-loaded PostgreSQL database client, but only the new AUXLIBS_PGSQL variable supports building a dynamically-loaded or statically-loaded PostgreSQL database client.

Failure to use the AUXLIBS_PGSQL variable will defeat the purpose of dynamic database client loading. Every Postfix executable file will have PGSQL database library dependencies. And that was exactly what dynamic database client loading was meant to avoid.

Then just run 'make'.

Configuring PostgreSQL lookup tables

Once Postfix is built with pgsql support, you can specify a map type in main.cf like this: 

/etc/postfix/main.cf:
    alias_maps = pgsql:/etc/postfix/pgsql-aliases.cf

The file /etc/postfix/pgsql-aliases.cf specifies lots of information telling postfix how to reference the pgsql database. For a complete description, see the pgsql_table(5) manual page.

Example: local aliases 

#
# pgsql config file for local(8) aliases(5) lookups
#

#
# The hosts that Postfix will try to connect to
hosts = host1.some.domain host2.some.domain

# The user name and password to log into the pgsql server.
user = someone
password = some_password

# The database name on the servers.
dbname = customer_database

# Postfix 2.2 and later The SQL query template. See pgsql_table(5).
query = SELECT forw_addr FROM mxaliases WHERE alias='%s' AND status='paid'

# For Postfix releases prior to 2.2. See pgsql_table(5) for details.
select_field = forw_addr
table = mxaliases
where_field = alias
# Don't forget the leading "AND"!
additional_conditions = AND status = 'paid'

Using mirrored databases

Sites that have a need for multiple mail exchangers may enjoy the convenience of using a networked mailer database, but do not want to introduce a single point of failure to their system.

For this reason we've included the ability to have Postfix reference multiple hosts for access to a single pgsql map. This will work if sites set up mirrored pgsql databases on two or more hosts.

Whenever queries fail with an error at one host, the rest of the hosts will be tried in random order. If no pgsql server hosts are reachable, then mail will be deferred until at least one of those hosts is reachable.

Credits