Haraka!

Take back control of your email with this easy-to-deploy mail server in a box. Mail-in-a-Box turns a fresh cloud computer into a working mail server.You get contact synchronization, spam filtering, and so on. On your phone, you can use apps like K-9 Mail and CardDAV-Sync free beta to sync your email and contacts between your phone and your box. And in your browser:

Sendmail is a general purpose internetwork email routing facility that supports many kinds of transfer and delivery methods, including the Simple Mail Transfer Protocol (SMTP) used for email transport over the Internet. A descendant of the delivermail program written by Eric Allman, Sendmail is a well-known project of the free and open source software and Unix communities, and has spread both as free software and proprietary software.

OpenSMTPD is a FREE implementation of the server-side SMTP protocol as defined by RFC 5321, with some additional standard extensions. It allows ordinary machines to exchange e-mails with other systems speaking the SMTP protocol.