I've had a lot of complaints this week from users who said Outlook.com stopped syncing in Outlook. One told me he received an email from Microsoft telling him to reconnect. So he did… using manual setup to add it back as an ActiveSync account. Another user tried to add the account using Outlook Connector.
In both cases, the users received error messages because those account types no longer work with Outlook. The Outlook Connector ceased working when the account was migrated to the new servers. Exchange ActiveSync no longer works in Outlook 2013 and 2016 as Outlook desktop was blocked as an ActiveSync client for Outlook.com. Outlook connecting using ActiveSync was always blocked on the business side and in on-prem Exchange servers but allowed in Outlook.com, to make the migration seamless for end users. With the migration all but finished, EAS support for Outlook desktop was disabled.
The only way to connect Outlook to Outlook.com accounts going forward is by using auto account setup to add the account as an Exchange account. (POP and IMAP are also supported, but do not sync calendar & contacts). If you are using an address that is not owned by Microsoft to log into Outlook.com, you will need to create an Outlook.com alias then use that to log into Outlook desktop.