I'm not sure what your asking for...
Are you looking for an ISP that will host your mail for you?
There are more ISPs than most people can comfortable shake a stick at. Since there are so many and some are regional I'm not sure that anyone can recommend one to you unless they are in your area.
OR
Are you looking for software recommendations for running your own server?
If you are looking for software it would depend on your budget. Microsoft Exchange works pretty well bu has a pretty steep price tag. Post fix is "free" (Postfix.org) and is Open Source.