Update: The full timeline for retirement of Basic Authentication in Exchange Online is now published in Basic Authentication Deprecation in Exchange Online – September 2022 Update.
In about 150 day...
Updated Sep 01, 2022
Version 5.0
Blog Post
jnolan62 If you have read this blog, you would have known that SMTP Auth will not be effected with this action. So you don't have to worry about your MFP's.
And I quote a part of this blog:
We’re turning off Basic Auth for the following protocols: MAPI, RPC, Offline Address Book (OAB), Exchange Web Services (EWS), POP, IMAP, Exchange ActiveSync (EAS), and Remote PowerShell.
We are not turning off SMTP AUTH. We have turned off SMTP AUTH for millions of tenants not using it, but if SMTP AUTH is enabled in your tenant, it’s because we see usage and so we won’t touch it. We do https://docs.microsoft.com/exchange/clients-and-mobile-in-exchange-online/authenticated-client-smtp-submission you disable it at the tenant level and re-enable it only for those user accounts that still need it.
If Microsoft disabled SMTP Auth due to little activity you should be able to turn it back on via Powershell:
https://docs.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/authenticated-client-smtp-submission
According to the previous blog:
I can’t re-enable SMTP using this feature, but I can request an opt out – huh?
Well spotted! We didn’t build logic into the re-enablement tool for SMTP as https://docs.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/authenticated-client-smtp-submission, but we wanted to make sure you could request an opt out for disabling of SMTP AUTH, so we included it here.
https://techcommunity.microsoft.com/t5/exchange-team-blog/basic-authentication-and-exchange-online-september-2021-update/ba-p/2772210