One of the most popular posts ever on this blog was the one we wrote in June previewing the new Yahoo Mail. Well, if you’re one of those apparently thousands of people who’ve been waiting anxiously to get your hands on it, your wait may soon be over. Yahoo told us today that they’ve finally opened the new service in beta “to a limited group of Yahoo! Mail users.” No, we don’t know who is and isn’t getting it, except to say that it’ll include a mix of free and premium users and all the old Oddpost mail users. The service will be “broadened to include additional Yahoo! Mail users worldwide in the coming months.”

The interface has changed a bit since we last saw it in June (click on the screenshots below). Originally, the new Yahoo Mail was going to open in its own window with no browser chrome, as Oddpost did, giving it the feel of an application that lived outside the browser. But testers didn’t like that, said Yahoo Mail product manager Ethan Diamond, so it now opens in a regular browser window.

Other features:

– New messages open in new tabs, meaning you can return to your in-box or go to another messaage without having to close the messages you have open.

– The new version will include Yahoo’s new search capabilities, but not PhotoMail for now.

– Shortcuts: it’s got several, but they don’t use the commad/control keys because those might conflict with browser shortcuts. So to compose a new message, for example, it’s “n,” not “Control-N.” You can mouse over the command buttons to see the shortcuts.

– Like Gmail, the in-box refreshes on its own, about every 10 minutes for now.

One feature we’ll be interested in monitoring is the one that lets users have their entire in-box open in one window, regardless of how many messages they have. (In the current Yahoo Mail and most web mail programs, users can only view 20-100 messages at a time.) The new Yahoo Mail doesn’t actually fetch all the headers in your in-box. That would take too long. Instead, it fetches the ones you need now and some of the ones you’d need if you scrolled down bit. How this will affect perfomance will be interesting to watch.

Diamond said Yahoo will start a “rolling introduction” of the new interface tonight. Oddpost users should have already received a message inviting them to join the beta.

Diamond said the new interface was built for the masses, the 200 million Yahoo Mail users around the world, not Silicon Valley tech fiends.

“Our goal with this was we wanted to make it so that those millions of people will immediately know how to use it,” he said.

Next up, the new Hotmail?