Microsoft will be removing the ability to add new accounts to Outlook on the web using the Connected accounts feature in September 2018.
You won’t be able to connect new accounts after September 15, 2018.
Accounts that were connected before September 15th will continue to sync as usual until October 30, 2018. On October 30th, all connected accounts will stop syncing email.
On November 15th, the Connected accounts option (Settings > Mail > Accounts) will be removed from Outlook on the web .
Email that has already synced will continue to appear in your inbox unless you remove it manually.
Yes, please review Microsoft's release on this change.