Programs for remote mail service via POP or IMAP contains free software for POP clients, servers and utilities. IMAP and POP perl client libraries. Qpopper free POP3 server and pop password server from Qualcomm. Many people have written utilities for it. It definately seems to be worth checking out.
Commercial support is available.
Trial server software and free client software. Majordomo is great freeware and in wide use. Written in Perl. ListProcessor freeware from bu.edu. ListProcessor commercial product is based on the free package.