CleanMail is a complete SMTP/POP3 email security solution that fights against spam and viruses. It works with any mail server like Microsoft Exchange 2003/2007/2010, Microsoft Small Business Server (SBS) 2003/2008, Lotus Notes/Domino, or IMail. CleanMail includes a comprehensive set of filters, including an attachment blocker, remote blacklist filter (DNSBL), and a complete build of SpamAssassin.
Synovel Collabsuite provides email, calendaring, and instant messaging solution for enterprises. It consists of a Linux email server with calendar and IM, a Web-based administration panel, a desktop client suite that runs on Windows and Linux, and AJAX-based Web mail access. It uses open standards for communications: IMAP, POP, and SMTP for email, CalDav for calendaring, and Jabber for IM.
Melon MailServer is a simple mail server emulator for developers. It can emulate POP3 and SMTP services. The SMTP facility receives and stores all the messages sent to it rather than sending them. The POP3 facility allows you to download any messages without authorization. The server is designed to accept all messages for any email accounts. It can be very useful for testing Web applications and other software applications.