The purchase of the iOS and Android e-mail app maker could signal that Microsoft is planning a native mobile email app for Outlook.

Continuing its cross-platform push, Microsoft has purchased San Francisco-based email app vendor Acompli.

Microsoft officials accidentally tipped their hand last week regarding Microsoft's intentions to purchase the startup by a blog post that was picked up by RSS readers before Microsoft could delete it.

In a December 1 blog post announcing the deal, Microsoft officials are not disclosing how much the company paid for Acompli.

"In a world where more than half of email messages are first read on a mobile device, it's essential to give people fantastic email experiences wherever they go," said Microsoft Corporate Vice President Rajesh Jha, who heads up Office 365 and Outlook, in today's blog post.

Acompli, headed by former execs from Zimbra and VMware, launched an iOS version of the company's email app in April, and an Android version in September. The mobile Acompli application features an integrated calendar, as well as Microsoft Exchange -- and, interestingly, Gmail -- integration.

What will Microsoft do with Acompli? For now, it's hard to say.

Microsoft officials were insisting that Outlook Web App was the only/main way that iOS and Android users could get Outlook with Exchange integration. Outlook Web App seemed to be where Microsoft was putting its mobile Outlook focus, at least until now.

But a number of iOS and Android users have not found Outlook Web App to be a great offering. So maybe Microsoft is planning to rethink its mobile Outlook strategy and make some kind of native mobile email app based on Acompli technology its new cross-platform offering in the enterprise mail space.