They'll have to point their MX records at you if you run your own in and out servers, or at Google Apps or Fastmail or similar if you outsource.

http://en.wikipedia.org/wiki/MX_record

Buy yourself a play domain, get a new gmail account, and set things up so that you appear to be your play domain while you use gmail. Then decide.

If you don't outsource, you probably don't need a server on each VM, but I suppose that depends in part on your contracts. But think about it, I use my own domain at gmail and Google doesn't maintain a mail server just for me.