If you're still looking for guidance on how to setup an email server using Amazon EC2, I've written a guide for it. Even though some find using ec2 for email to be a hassle it doesn't have to be for you.
https://avix.co/blog/server-hosting
Here are some details about what the configuration will give you;
The system uses:
-Postfix as the smtp agent
-Dovecot as the client-side connect and mailbox manager
-Postgresql database to handle mail users, mail transports and the Spamassassin database
-Amavis (w/ Clamav & Spamassassin) for protection against viruses sent through email, and to facilitate an adaptive spam detection system that learns and corrects its behavior for each individual user
-Spamassassin as the spam filter and bayes to learn spam from ham and ham from spam
-Apache as the web setup, enables http & https connections to your site
-Squirrelmail as the default webmail. After the server is setup you will be able to check your email on yourdomain.com/mail from any browser on any device
The system supports:
-Multiple transports for different domain
Good luck, and let me know if I can clarify anything.