At the moment, you can only select a single Gmail account to sync with Outlook, which could be frustrating since so many people use multiple Gmail addresses. This isn't the first time the two competitors have joined forces. In 2017, Microsoft added Google Calendar and Contacts functions to its desktop-based version of Outlook 2016. As testing continues, more Outlook users could have the feature applied to their accounts. We've reached out to Microsoft for clarification and will update this post if we hear back.

Update: Microsoft has confirmed the test, with a spokesperson telling Engadget "We are always looking for new ways to extend the best email experience to our customers and can confirm that we're experimenting with a small set of Outlook.com users to learn and gather feedback."