Updated at bottom with some clarifications.
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.
Frankly, it's a shame that Zimbra ended up with Yahoo, which has 92.5 million mailboxes. Though Zimbra is a standout in the industry, Yahoo's own strength in consumer e-mail likely keeps Zimbra in second place for resources internally, especially since Zimbra's enterprise-grade e-mail may not be a tight strategic fit. Zimbra would have been an exceptional match for Apple or Adobe with their design-savvy customer bases.
What's done is done, however, and Zimbra will just have to settle for getting 40 million paid mailboxes while others can hardly give that many away for free. It's a tough job, but someone has got to do it.
UPDATE: I should have pointed out that the Gmail numbers relate to U.S. totals. It wasn't my intent to mislead on that; I simply failed to call it out, and apologize. Also, as pointed out in the VentureBeat story, to which I linked, none of the numbers - Google's or Zimbra's - are absolutely to be relied upon, as ComScore numbers can be inaccurate and Zimbra's are self-reported. Even so, Zimbra's progress is impressive.
A commentator below rightly points out the difference between active users of a service and the raw number of mailboxes sold (in Zimbra's case). This is a useful, but not dispositive, point. If anything, it probably affects Gmail's reported numbers more negatively than Zimbra's.
At any rate, which problem would you rather have: paid but inactive users or freebie inactive users? I'm guessing that Zimbra will happily take the former, and work to innovate more to turn passive accounts into active users; otherwise, Comcast and other customers simply won't renew their subscriptions.
As for the source of the 20-million user jump for Zimbra, some of this comes from bring the Comcast users online with Zimbra. Zimbra announced the deal in 2007 but that there's a big time gap between closing a deal and deployment.
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