Forum OpenACS Q&A: Response to Web Mail
If you are in a rush to put something up why not try Horde.org's IMP project?
From what I understand it can be made to use Qmail (an ACSer favorite) and PostgreSQL (a OpenACSer favorite).
It will not store email in the DB though. But all accounting info seems to be redirected to the RDBMS. You could try to modify the PHP to Tcl and save some design work front-end building wise.