eMailman - Enables using third party e-mail programs to receive or send AOL mail.
i.Scribe/InScribe - A lightweight cross platform email client, supporting POP3, IMAP4 (fetch), [E]SMTP, SOCKS5, and MIME with an integrated contact database and calendar.
Mahogany - An OpenSource cross-platform mail and news client available for X11/Unix and MS Win32 platforms, supporting SMTP, POP3, IMAP, NNTP, and full MIME support.
Mozilla Mail/News - Technical information and project documentation of the integrated email and news client in the Mozilla Suite.
OpenSmtp.Net - An SMTP component written in C#. Allows developers to use SMTP servers other than MS SMTP and has a web service that allows the sending of email via HTTP/SOAP. [BSD License.] Windows only.
SimpleMail - A new mailer for the Amiga platform (both classic and OS4) and compatible systems (MorphOS).