zoho offers free custom domain email hosting. It's also surprisingly good, the UI/integration between the pieces is very well done.
I tried Zoho last year after hearing multiple recommendations and it was nothing but problems with spam coming in and my outbound emails being incorrectly marked as spam. I even had SPF + DKIM tested and working from the start! Not sure I would try them again after that experience.
Doesn't seem to support addresses from other domains though.