Hot on the heels of a day of rumors, VMware announced the acquisition of Zimbra, the open-source email platform vendor previously purchased (and up until now, still owned by) Yahoo!.

It’s a somewhat puzzling acquisition. Its key strategic thrust seems to be enabling the service provider ecosystem. Most service providers (i.e., hosters) already offer email as a service — although today, they primarily offer Hosted Exchange. Other platforms — Open-Xchange, OpenWave, Critical Path, Mirapoint, etc. — are used for more commodity email services. Relatively speaking, Zimbra doesn’t have as much traction in the service provider space, and VMware’s service provider ecosystem is not gasping for lack of reasonable platforms on which to offer email SaaS.

The email SaaS space is super-competitive. Businesses have come to the realization that email is a commodity that can be safely outsourced, and that huge cost savings can be realized by outsourcing it; this is driving rapid growth of mailboxes delivered as SaaS, but it’s also driving aggressive price competition. That, in turn, drives service providers to push their underlying email software vendors for lower license costs.

One has to speculate, then, that this acquisition is not just about email. It’s about the broader platform strategy, and the degree to which VMware wants to own an entire stack.

My colleagues and I are working on publishing a Gartner position (a “First Take”) on this acquisition, so I’m sorry to be a bit brief, and cryptic.