There are many mail howtos on the web ... can one more hurt?
http://rob0.nodns4.us/howto/README
http://rob0.nodns4.us/howto/
http://rob0.nodns4.us/howto/latest.tar.gz (all files)(Sorry, not HTML yet. That is on the agenda.)
This is a multiple address class sample implementation of a Postfix MTA and Dovecot IMAP server using a SQLite3 data backend. Domain lookups, user maps, access and transport maps: all using a single, shared SQLite database file.
What, other than the SQLite backend, distinguishes this from other mail system howtos?
The Postfix high points include a complete implementation of all address classes and per-address transport(5) maps, virtual(8) UID/GID maps, and smtpd(8) recipient access(5) maps. (The latter is using smtpd_restriction_classes, which are not discussed in detail, but are implemented in an interesting way.)
On the Dovecot side, it's mostly standard stuff. The SQL deny userdb implementation, and the seamless integration of system and SQL users, might be interesting.
I think the database itself is the best part of this example. It's as close to "normalized" as I think it can reasonably be. A significant fact is that each revision of the system has tended to simplify the schema. That's a good sign, I think.
One central Domain table lists all domains and hostnames to which the server makes reference. Likewise, a central Address table lists all addresses (with a pointer to the Domain table for each record.) The Alias table defines relationships between Address entries. (Both local(8) and virtual(5) alias maps exist in that table.)
Comments and suggestions are welcome, on-list if it's topical to whichever list (please don't crosspost unless comments are relevant to both lists), or offlist to the address in the README file (or as detailed below.) Thanks for your interest.
http://rob0.nodns4.us/ -- system administration and consulting Offlist GMX mail is seen only if "/dev/rob0" is in the Subject: