Microsoft is to end support for Exchange Server 5.5 by the end of the year and is urging users to upgrade to Exchange Server 2003.

According to Microsoft, the number of Exchange Server 5.5 users dropped by about 40 percent over the past year, evidence that customers have been upgrading in anticipation of the product phase-out.

Microsoft has also reminded customers that Exchange Server 2000 will move out of mainstream support into extended support at the end of 2005. Mainstream support includes free incident support, security updates and non-security hotfixes. Once Exchange Server 2000 moves into extended support, customers will have to pay for support and non-security-related hot fixes.

The company also will not accept requests for warranty support, design changes or new features during a product's extended support phase. Extended support only applies to business and development software products; it does not apply to consumer, hardware or multimedia products.

Microsoft recently released a second service pack for Exchange Server 2003 that the company said has better support for mobile e-mail - including technology that pushes e-mail from Exchange direct to mobile devices.

The company said it plans to release to manufacturing the next version of Exchange, code-named Exchange 12, sometime at the end of 2006 or early 2007.