In a surprise announcement today, Microsoft released a new version of Outlook for the Mac. The new version requires an Office 365 subscription to be activated.

The news came in a blog post from the Office 365 team, which promised that the new version would deliver "improved performance and reliability and a fresh look and feel that is unmistakably Microsoft Office."

The new version number, 15.3, syncs with the latest major version numbers for Outlook's Windows counterpart, which is currently at 15.0.4659.1001.

The new Outlook supports Exchange Online accounts for Office 365 commercial subscriptions as well as Outlook.com (formerly Hotmail) accounts paired with Office 365 Home and Personal subscriptions. It also supports IMAP accounts, including Gmail. As with Outlook 2011, each account gets its own top-level node in the folders list.

According to Microsoft, the new release includes performance and reliability improvements from an improved threading model and database structure. It also includes improved support for categories (with syncing between online and Mac category lists), searching for online archives, and Office 365 push email support.

The new release is available as a download from the Office 365 portal for signed-in subscribers. It's worth noting that Microsoft recommends uninstalling Outlook 2011 for Mac "for the best experience." [Update: The Office team says they're working on clarifying these support documents. Both Outlook 2011 and the new Outlook can coexist and will share the same preferences. They recommend removing the Outlook 2011 shortcut from the dock to avoid confusion.]

The new Outlook is not available for Office users who have purchased a perpetual license to Office 2011 for Mac or Office 2013 for Windows.

In other Office for Mac news, Microsoft detailed its roadmap for the next release of Office.

In the first half of 2015 we will release a public beta for the next version of Office for Mac, and in the second half of 2015 we will make the final release available. Office 365 commercial and consumer subscribers will get the next version at no additional cost, and we will release a perpetual license of Office for Mac in the same timeframe.

That timing is in line with the probable release dates for Windows 10 and the next version of Office for Windows, suggesting that a very big upgrade cycle is in the works for next year.