Well, I don't know if you'll get both in a single free package... there are plenty of free IMAP providers out there, so google for "free IMAP" and just use GPG for encryption.
You also might want to check out
Hushmail. They'll give you a free account with encryption, but you'll have to pay $30/year if you want IMAP access (actually, they're having a promo right now.
50% on IMAP for one year).
Good Luck!