The latest upgrade to what is fast becoming one of Microsoft's principal products will be released for download Friday, with significant new features including a long-sought disaster recovery tool.

One of the changes e-mail administrators had been wanting since the era of Microsoft Exchange Server 2003 concerns replication -- the ability to source the e-mail database at multiple physical locations simultaneously. Exchange has always had this feature, especially on the local level, but effectively managing it has been a matter of tricky scheduling.

Now, one of the features that was originally anticipated for the initial release of Exchange Server 2007 makes its premiere appearance with SP1: standby continuous replication (SCR). Customers have already been beta testing this feature, and tomorrow, the testing will be officially complete as ES2007 SP1 becomes available for download.

The basic concept behind this new feature is actually quite simple: It enables Exchange's e-mail database to continue to be replicated locally, just as before in an active mode, while at the same time a separate level of replication happens remotely, in a passive mode. In case of a disaster, failover is as simple as flipping a switch, making the secondary passive data cluster into the primary active cluster.

Microsoft warns that SCR should only be used for replicating e-mail folders, not the public folders that make accessible shared documents and schedules -- those will continue to follow a separate replication scheme altogether.

The new replication scheme will force some admins to implement one difficult migration plan, specifically with regard to clustered mailbox servers in Windows Server 2008. Failover clusters supported by WS2K8 will be very different than those for Windows Server 2003, and the upgrade process will not be automatic. So rather than upgrade the database on the clusters, admins will have to build new failover clusters on WS2K8, and move the mailboxes between the old and new clusters manually using PowerShell commands (cmdlets).

It's not an unanticipated situation, and admins have already had a year to get accustomed to doing laborious tasks with PowerShell.

Being able to securely administer e-mail for minor or major disasters without all the laborious replication that currently exists, could play a role in reducing Exchange Server 2007's rising total cost of ownership. A December 2003 study by electronic messaging analysts The Radicati Group determined that, over a three-year period, an enterprise would spend on average $107.02 per user per year managing just the messaging portion of Exchange Server 2003, versus $150.55 per user per year for Lotus Notes/Domino.

That gap closed substantially, when a May 2007 Radicati study (PDF available here) concluded the three-year messaging TCO cost for Exchange Server 2007 had risen to $145.86 per user, per year -- at a time when Lotus' TCO costs could conceivably have fallen.

In turn, the impact of improved and conceivably simplified replication (after the migration takes place, that is) could be measurable, and a Radicati study on ES2007 SP1 will be very interesting to read.

Microsoft has also noted that a new version of Forefront Security for ES2007 SP1 will be made available starting today.