Less than a year after Zimbra launched its open source email platform, more than 1,000 customers have deployed 5 million Zimbra inboxes.

Roughly half of Zimbra’s revenue comes from channel partners and managed service providers, but Zimbra hopes to push that figure as close to 100 percent as possible, according to Jim Morrisroe, VP of sales, and John Robb, VP of marketing and product management. Instead of competing head-on with Microsoft Exchange, Zimbra is targeting the 50 percent of the email market that Microsoft doesn’t control.

Zimbra’s browser-based email client runs on Web 2.0 technology and resembles a full-blown 32-bit Windows application in design and functionality. The company is working with other open source providers (such as Asterisk) to build hooks between email, calendaring and VoIP technology.

The VAR Guy and Zimbra both expect VARs to move up the open source server stack in 2007. However, Zimbra is taking a “wait and see” approach to partnering with server stack providers such as SpikeSource.

Zimbra considered a relationship with SpikeSource and expresses respect for the company. But another open source email provider–Open-Xchange–ultimately partnered first with SpikeSource.

Still, Zimbra doesn’t seem to be suffering. Selling five million inboxes in roughly 10 months is no small feat.