As Microsoft is completing the migration of the Outlook.com mailboxes to the Office 365 platform, they have begun turning off Exchange ActiveSync (EAS) support for Outlook.
This will only affect you when you are using Outlook 2013 or Outlook 2016 and haven’t configured your Outlook.com account as an Exchange account yet.
To check this, go to;
File-> Account Settings-> Account Settings
When it says Microsoft Exchange behind your account, you don’t have to take any action. When it says Exchange ActiveSync, you’ll have to re-add your account via Auto Account Setup by supplying your name, email address and password (or App Password). So don’t choose the Manual Setup!
After this, you’re good to go again and you can remove the Exchange ActiveSync account and enjoy the improved synching process and support for features such as; Drafts sync, Contact Groups, Follow Up Flags with Reminders, sending as any of your Outlook.com aliases and a whole lot more.
If Auto Account Setup fails, check for a solution in the guide; Account Setup fails for Outlook.com accounts.
Note: EAS will only be disabled for Outlook on the desktop. You’ll still be able to use EAS connections in any of your other Mail apps such as on your smartphone or tablet.
Why now and whap happens when I don’t do this?
The reason why Microsoft is doing this now is because there are various bugs with EAS that only apply to Outlook desktop and have recently begun escalating. The target always has been to disable EAS for Outlook desktop at some point and apparently that point has been reached now.
If you don’t reconfigure your account before they turn off EAS Outlook desktop support for your mailbox, the sync will stop and you’ll get a message in your Outlook.com mailbox (which you can always still access via an Internet browser) with more info and instructions to reconfigure your account as an actual Exchange account.