I used iRedMail to setup department mail server and it just worked. I had no problems with configuration: IMAP, SSL, SMTP - everything works out of the box. Spam protection is also adequate, at least for a relatively low-volume usage.
You're not addressing what majelix mentions. How about DKIM? SPF? Do you know if/when you end up on any block-lists? What about deferrals from the major providers?
It is by no means impossible that everything "just works" for you, but depending on your e-mail patterns, and what ISP you uses, and whether or not there's any spammers or spammer-look-alikes on the same netblocks as you, the level of hassle in ensuring your outbound e-mails actually gets delivered to your recipients inboxes rather than spam-filtered can be immense.