@IGMIGMIMXMD
By looking at this MS articel it seems that SMTP AUTH is still available as it was only disabled in tenants where it wasn't being used. Only Basic authentication in Exchange Online for Exchange ActiveSync (EAS), POP, IMAP, Remote PowerShell, Exchange Web Services (EWS), Offline Address Book (OAB), Autodiscover, Outlook for Windows, and Outlook for Mac was removed.
We also use O365 Exchange internally for FSM testing and facing no issues as of yet. Could you issue be realted to something else? Did you check the FSM Server Logs when trying to send notifications?
My idea isn’t implemented yet because we have to ensure that backward compatibility is still given when enhancing the system to use OAuth2 as well for SMTP. That’s why it’s still in the backlog and under investigation.
Best regards
Roman