I too am looking for an email host for a couple domains that may not need any immediate websiting.
If you're looking for unlimited POP3 accounts, I suspect that will be either hard to find, or quite pricey.
On the other hand, the FQ "parking" package provides one POP3 account with "catch-all" addresses for the parked domain. I'm inclining toward this myself, while pondering whether or not an IRM would be a workable tradeoff for some site space.
At present I don't have the email features of the registrars (dotster and enom) working yet. ;(