One of the drawbacks of Microsoft's Hotmail replacement Outlook.com was that if you wanted to use something other than its web interface, email clients could only access messages using POP3 or Microsoft's EAS protocol. A lot more devices and services use IMAP, and now so does Outlook.com.
This means you can access your Outlook.com in, say, Thunderbird using IMAP, which offers a few key advantages, such as syncing sent items and other folder changes.
In addition, it means third-party apps such as TripIt, OtherInbox and Slice can connect to your Outlook.com email to enable features such as tracking your travel itineraries, keeping your inbox organised, and gathering all your receipts.
Along with the introduction of IMAP, Microsoft has also made the authorisation for both IMAP and SMTP to OAuth 2.0. That means apps and services that connect to Outlook.com may be more secure, since they require your authorisation.
Check out the changes and the settings for IMAP in Microsoft's Outlook Blog.
Oulook.com now has IMAP [Outlook Blog]