Axigen is an integrated email, calendaring and collaboration platform, built using a unique mail server technology, for increased speed and security. The FREE edition is intended for businesses looking for a great all-in-one alternative to open source, offering advanced mail services for 100 users (including 5 calendaring users) and a large set of available add-ons.

The Axigen Free Mail Server is offered as a yearly license for unlimited domains, with forum and knowledgebase support, available for Windows Server 2003/2008 operating systems.

High-performance mail server technology & more:
-Fast & secure email transfer, processing & delivery
-Backup & restore module
-Effortless administration (Web-based)
-Performance reports & statistics

WebMail access from PCs & mobile phones:
-Skinnable & multilanguage Standard WebMail Interface (fast & friendly, easily brandable & localized in over 20 languages)
-Desktop-like Ajax WebMail Interface (keyboard navigation & shortcuts, drag-and-drop, email filters, support for localization)
-Mobile WebMail Interface
-Email messages retrieval from external accounts (e.g. Yahoo! Mail, Gmail)

Efficient time management tools:
-Calendaring for 5 users - via Personal Organizer (including Calendar/Tasks/Notes, iCal/Webcal access)
-Address book (personal, public & domain contacts)
-User groups, mailing lists
-Fast, index-based search

Advanced server security:
-Multiple AntiVirus & AntiSpam support
-Authentication & Encryption
-SPF & DomainKeys compliance
-Country Filtering

Available add-ons:
-Personal Organizer (additional calendaring users)
-Outlook Connector (fast, localizable, includes offline work)
-Extra Security (Commtouch Real Time AntiSpam & AVG AntiVirus/AntiSpam)
-24x7 Technical Support

For more info, visit: http://www.axigen.com/mail-server/free/