It is very straight forward configuring LDAP support into Postfix. There are three steps:

1) compile LDAP support into Postfix
2) edit /etc/postfix/main.cf
3) add the relevent routing & alias data to your LDAP server.

1. Postfix does not enable LDAP support by default, but it's pretty easy to do.

If you are running a recent version of RedHat & use Cyrus IMAP, you can grab my RPM package here: ftp://k12linux.mesd.k12.or.us/pub/postfix-LDAP

If you want to compile it by hand, here's the proper build magic:


make makefiles CCARGS="-I/usr/include -DHAS_LDAP" \
  AUXLIBS="/usr/lib/libldap.a /usr/lib/liblber.a"
make

2. edit /etc/postfix/main.cf to point to your LDAP server for it's alias maps:



alias_maps = hash:/etc/aliases, ldap:ldapsource
ldapsource_server_host = ldap.mesd.k12.or.us
ldapsource_search_base = dc=mesd,dc=k12,dc=or,dc=us
ldapsource_query_filter = (&(mail=%s)(!(|(maildrop="*|*")(maildrop="*:*")))


alias_maps tells Postfix to look in /etc/aliases first, and then query the LDAP server as specified by the ldapsource lines.
ldapsource_server_host specifies the LDAP server
ldapsource_search_base specifies where in the LDAP heirarchy to search
ldapsource_query_filter is not required, but is recommended to prevent programs from being specified as an alias - which has dire security consequenses.

3. A typical /etc/alias entry looks like this:

eric_harrison eharrison

which tells Postfix to accept mail addressed to "eric_harrison" but deliver it to the mailbox of "eharrison". The same concepts can be added into the LDAP directory with the attributes mailacceptinggeneralid and maildrop

mailacceptinggeneralid=eric_harrison
maildrop=eharrison

If you'd like more details, take a look at the documentation shipped with Postfix: LDAP_README

Feedback & additional documentation would be more than welcome!
Eric Harrison