Zimbra, Yahoo's open source messaging and collaboration software company whose fate was unclear if Microsoft had bought Yahoo, says it's got a new open extension framework for its Collaboration Suite (ZCS) that will enable two-way interoperability with Microsoft Exchange.

It expects the move to encourage large enterprises and academic institutions to explore Zimbra more.

The start-up's co-founder Satish Dharmaraj said, "Interoperability with Exchange and other leading collaboration systems is a top request by many enterprises and academic institutions where mixed deployments are common." Zimbra customers include Dai Nippon Publishing, Reliance Industries, H&R Block, and Texas A&M University.

The first extension, built by Zimbra for Exchange 2003 and now in beta, will let Zimbra access and share two-way free/busy information, schedules, and global address books with Exchange. Zimbra has been integrated with Active Directory, creating a unified Global Address List (GAL) of both ZCS and Exchange users in the same deployment.

Zimbra says the Zimbra community can write extensions to other collaboration platforms such as IBM's Lotus Domino and Novell's GroupWise.

The Exchange feature works in all Zimbra clients including Zimbra's AJAX Web Client, Outlook via Zimbra Connector for Outlook, Zimbra Mobile supported devices such as BlackBerry, and Windows Mobile-based smartphones. Exchange users can use whatever client they use currently such as Outlook.

ZCS Interoperability for Exchange doesn't require any changes on the Exchange server; the service is managed in the Zimbra Administration Console.

ZCS Interoperability for Exchange is free for all ZCS Open Source and commercial Network Edition users. Zimbra Outlook Connector and Zimbra Mobile are available for ZCS Network Edition users.