In its Beta 3 release of Zimbra Desktop today, Yahoo has added free IMAP access and other new features to its crossplatform software, geared at competing against e-mail clients such as Microsoft Outlook and Mozilla Thunderbird by working as both a standalone desktop application and an online e-mail interface.

Based on technology obtained through Yahoo's Zimbra Software buyout in 2007, Zimbra Desktop can now provide e-mail access and offline synchronization to Yahoo Mail users on a choice of Windows, Linux, or Mac OS.

"It's an offline capable client so you can take your data with you whenever you don't have internet access - then sync any type of interaction that you can do in normal webmail access when you get connected again." said Yahoo's Mike Morse, in a blog posting today.

Zimbra Desktop uses Java for crossplatform operability, along with Ajax browser technology for an enriched user interface.

Since the release of Beta 2 in April, Yahoo has broadened IMAP access to all users, not just those with "plus" accounts, enabling access not just to Yahoo Mail but also to other accounts such as Gmail and AOL that use IMAP or POP.

"There's now IMAP access through Zimbra Desktop to all free, plus, and business accounts," he said. "Normally only plus accounts have POP access, but as a perk when using Zimbra Desktop the mail is synced via IMAP; which is a much better protocol for keeping your mail organized - and yes it's available to free accounts as well."

New folders let you take "tasks, documents and briefcase items with you wherever you may roam," Morse said. Also new are an icon badging feature which displays the number of unread messages, and an autostart capability for checking to see whether the background service is running -- and automatically launching it if it isn't.

Autostart "proves especially useful on Linux since the service doesn't automatically start after reboot," Morse explained.

For Windows and Mac users, Zimbra Desktop now includes a link handler, which brings up Zimbra Desktop's composer with a Javascript call, along with new built-in mail and appointment notifications.

"Zimbra Desktop on Windows now takes advantage of the native tray icon bubbles and on Mac of course we use Growl," Morse said in his blog.