[mstrem]

This is typical, I have just done the whole process myself a few weeks ago from scratch (fresh CentOS install) and now this comes up.

However I do not regret it at all. I had Linux experience and it took me one day and a half work to get it all working very nicely.

I am happy with my config: Postifx, Dovecot, RoundCube, SpamAssassin, ClamAV

Server supports unlimited domains and user accounts - SSL is required for all connections, I only allow IMAP and I have configured it with two valid free StartSSL certificates:

    One under mail.domain.com (for email clients)
    One under webmail.domain.com (for the webmail)

And both of course do not show warnings and green padlock is always nice.

The thing that scared me the most was outgoing emails being dropped - however to date I have delivered fine to all main email provider - followed a few simple rules:

    Ensure you have both SPF and TXT correct DNS records
    Ensure you have IPv6 configured properly (Google was  rejecting due to this) 
    Set your reverse DNS
    Set your machine hostname etc. in postfix

[dav-]

You seem to have learned a lot in the process. Can you point to any good resources that helped you, specifically with security concerns and outgoing mail reliability? I've already got a mailserver running with a similar setup as you, but I haven't invested much effort into security or making sure mail providers accept my emails (Gmail sometimes marks them as spam and AOL rejects them all together).