[exim] Suggested POP3 Server

I've been running Exim happily for several months for mailman. I now
have a request to setup an POP3 server on the machine to exchange mail
with another application coming into use. Having never used a POP3 or
IMAP server before I'm not sure how to pick the best to work with Exim.
I found a reference in the archive from over a year ago about this
issue, but I want to make sure I'm taking the latest advice. Anyone
have a strong recommendations for or against any particular POP3
servers? FOSS would be nice, but not essential.

Thanks
Aaron