Poste.io!

A fully fledged, free email server solution, an open source project (GPL v2).

Zimbra Collaboration is an open, secure collaboration tool for email, calendaring, tasks and more. With the most innovative web application available today, Zimbra boosts the productivity of users on any desktop and dramatically reduces TCO compared to legacy platform vendors.

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:

Foxmail is a free POP3 and IMAP4 e-mail client in English and Chinese for Windows systems.

Microsoft Exchange Server is a messaging and collaborative software product developed by Microsoft. It is part of the Microsoft Servers line of server products and is widely used by enterprises using Microsoft infrastructure solutions. Exchanges major features consist of electronic mail, calendaring, contacts and tasks; support for mobile and web-based access to information; and support for data storage.

Indian Webmail service allowing people to sign up for an @email.biz mail account.Cloud based Login and Multiple Login System give you safe and secure access to your POP / IMAP email accounts. Now access your email with any Web Browser, PDA or Mobile phone from anywhere in the world.

hMailServer is a free e-mail server for Microsoft Windows. Its used by Internet service providers, companies, governments, schools and enthusiasts in all parts of the world.

OpenChange aims to provide a portable Open Source implementation of Microsoft Exchange Server and Exchange protocols.

Turnkey Solutions for the Enterprise Cloud

Xeams is a secure & powerful mail server for Windows, Linux, Solaris, MacOSX and other flavors or UNIX, which supports SMTP, POP3, and IMAP. It includes a powerful spam/junk filtering engine that elimates up to 99% of junk email right out of the box. The software offers a flexible approach to email, making it a very user friendly server.