A customer of mine recently asked the price for some Linux email servers, since he wanted to upgrade his Exchange 5.5 infrastructure. I did some internet investigation and I ended up with a couple of products compatible with Outlook (well, sort of...). The good side of this experience is that it helped me to deconstruct a myth about Linux software: the licensing of the 2 products I proposed was more expensive than Exchange.
Microsoft has an excellent document about this subject: Comparing Exchange Server to "Low-Cost" and Commodity E-Mail Products.
Summary: Several e-mail vendors claim to offer inexpensive basic e-mail services that are integrated with Microsoft Office and Microsoft Office Outlook solutions but they cannot reliably deliver on this claim. Exchange Server, however, provides native integration with Outlook coupled with a high return on investment (ROI), low total cost of ownership (TCO), excellent networking and security integration with the operating system, extensive support from third-party vendors, and the highest level of research and development in the industry.
This document explains why Exchange Server-and not so-called "low-cost messaging" vendors-can meet your e-mail and collaboration needs regardless of the size of your organization.
Included in this document:
• Only Product to Offer Complete Native Support for Outlook
• High ROI Driven by Productivity and Low TCO
• Group Scheduling and Wireless Messaging
• Standard Protocols for Flexible E-Mail Solutions Across Your Organization
• Proven Scalability for the Largest Organizations
• Leading Integration with Windows Directory, Management, and Security Services
• Extensive Support from the Third-Party Vendor and Professional Communities
• Bottom Line