Xobni, the email service whose fans include Bill Gates, is getting ready to expand beyond its current Microsoft Outlook-only product. That’s a smart and obvious move, and the startup’s new service is particularly juicy for Internet rumormongers –Xobni plans to add compatibility with Yahoo Mail, including features that let you use Yahoo Mail and Outlook together, according to TechCrunch.

This news fits in nicely with a couple of acquisition stories that have been floating around. First, of course, there’s the continuing saga of Microsoft’s attempt to purchase Yahoo. But there have also been rumors that Microsoft wants to purchase Xobni for $20 million, although Xobni co-founder Matt Brezina told us it’s too early to comment. If the Yahoo deal (finally) goes through, it’s easy to see why Microsoft would want to own a startup that not only enhances Outlook, but connects Outlook to the very popular Yahoo Mail.

We were pretty impressed when we played with Xobni Insight last September. The San Francisco startup’s product helps you organize and navigate your email, primarily through a sidebar that shows you profiles of people you’re corresponding with. Soon, Xobni will give you the same functionality in Yahoo Mail, and also help you consolidate your past correspondence and contacts from both services. That’s going to be pretty useful, even if the acquisition rumors turn out to be little more than empty talk. It’s a good next step for Xobni — the company’s long-term plans probably include compatibility with as many email programs as possible. With its enormous popularity, Yahoo Mail is an obvious choice, not to mention the fact that Xobni brought on Jeff Bonforte, Yahoo’s former vice president of social search, as its new chief executive in February.