Services like posterous support blogging, etc through email. It seems, then, that any server they use (their headers indicate postfix) must support (a) only accepting email from whitelist based on say, web registration (b)support extensible handling of attachments (c) interaction with a database. How is this generally handled? With back-end smtp servers as worker daemons written in pyton or something else? Or are their capabilities scalably baked into postfix/qmail etc for these purposes?