It’s impressive to be able to give away 31.2 million free Gmail accounts, as Google has. It’s even more impressive to get customers to pay for 40 million mailboxes, as Zimbra reported today, representing a sharp spike from the 20 million paid mailboxes reported in early 2009.

The secret to Zimbra’s success? Innovation and integration, in part. While Google Maps has found its way into a range of different applications, Zimbra leads Gmail in mash-ups (called “Zimlets” in Zimbra parlance). My company is a Zimbra customer, and one of our sales engineers wrote a Zimlet to integrate Alfresco with Zimbra…in his spare time…over a weekend.

Yes, Zimbra is that easy to extend.

As for innovation, as just one example Zimbra beat Gmail to offline application access by two years. Not bad for a company with a fraction of Google’s employees (or PhDs).

As VentureBeat points out, Zimbra is now ahead of Gmail in unique mailboxes and only slightly behind Microsoft’s Hotmail service. That’s pretty impressive: one little open-source company takes on the two titans of software and wins (against Gmail), or shortly could win (against Hotmail).

Yes, the jump from 20 million to 40 million is likely due to Comcast’s decision to use Zimbra for its user e-mail accounts. But it’s still impressive.

via Zimbra tops Google’s Gmail with 40 million paid mailboxes | The Open Road – CNET News.