Sumolabs

Zimbra, an open source server and client technology for next-generation enterprise messaging and collaboration, recently reached 6 million paid mailboxes. As a robust and affordable alternative to Microsoft's Exchange Server, Zimbra has continued to move upmarket and achieved tremendous growth over the past six months.

Two versions of Zimbra are available: a community-supported open-source version, and a commercially supported version ("Zimbra Network") with closed-source components. This foundation in open source, and the contribution back to the open source community has made Zimbra extremely popular.

What makes Zimbra even more attractive to consumers is that it is compatible with proprietary clients such as Microsoft Exchange Server, Apple Mail, and so forth, in a way that mail, contacts, and calendar items can be synchronized from these services to a Zimbra server. They have also made is possible to 2-way sync to many mobile devices (BlackBerry and Windows Mobile).

Traditional corporate communication is changing, and Microsoft is well aware of this new player on the field. "They've done a good job," Bill Gates said about the product "doesn't even come close to the things that Exchange does."

Clearly Gates doesn't know about the classic low market disruption. Zimbra has come in low market, and will keep adding features (as Microsoft continues to ignore them). They will gradually capture more and more market share as their product matures and becomes even more affordable.

Zimbra has only 6 million of Microsoft's 140 million.

Let's see how fast they can swim upstream.