Exchange Online is retiring basic authentication which means, I think, that CiviMail will no longer be able to process bounced messages in Exchange Online mailboxes. Are there any plans for CiviMail Mail Accounts to use Oauth2 for authenticating with the mail server?
UPDATE: It's available now for INBOUND emails (bounce processing/email processor) in 5.32 as a hidden extension. See https://docs.civicrm.org/sysadmin/en/latest/setup/oauth/#enable-the-module
It's in progress for google and would likely be the same for outlook/exchange.
It supports using a bearer token already but we could use some coding help though for someone to write the code to get/store/use the refresh tokens in order to get the bearer token.