Microsoft in their infinite wisdom decided to disable basic auth for their hosted Exchange Online. Which is kinda unfortunate, since many apps and processes might still use their mailboxes and changing it might take some time. Say, if you have some old in-house app, you might need to rewrite it, add Oauth support to it. Quick solution for this is here:https://blog.rebex.net/office365-imap-pop3-oauth-unattended