Microsoft published the timeline and steps to take to finalize the retirement of basic authentication in Exchange Online:
You might need to take action to avoid disruption of access. A very short summary:
-
All previous opt-outs and re-entablements of basic authentication are not valid anymore
-
If you want to keep using basic auth in Exchange Online after October 1st, you must explicitly opt-out in September
-
Basic auth is getting disabled for any protocols not opted-out during September, starting October 1st
-
All opt-outs (or later re-enablements) expire early January 2023
If you are still using basic authentication for any of affected protocols, you must take action in September and finish your migration to modern authentication by early January 2023.
