I switched twice, from my own mail server -> gmail -> back to my own server. Setting up the mail server the second time around was much more difficult for me. There seemed to be a lot more to get right this time around. (anti-spam, in particular. Ensuring that your mails aren't dropped by other servers can be a pain to get right).

I found http://www.mail-tester.com/ to be very useful.

That's awesome, thanks for the link.