Office messaging server is a high capacity, easy to administer sendmail replacement. Supports SMTP and POP3, list management, web-browser interfaces. Free trial download. PMDF from innosoft international, inc. Works with PC mail systems, POP, IMAP, X.400, SMTP, MIME, pagers, printers, UUCP, mailing lists, and more.
Postfix is a free alternative to sendmail.
Postfix attempts to be fast, easy to administer, and secure, while being sendmail compatible. 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.