Red Hat Single Sign-On sends emails to users to verify their email addresses, when they forget their passwords, or when an administrator needs to receive notifications about a server event. To enable Red Hat Single Sign-On to send emails, customers need to provide Red Hat Single Sign-On with their SMTP server settings.
When the SMTP server requires authentication, then there is a Basic Authentication happening with a Username and Password.

Starting on January the 1st, 2023, Microsoft has announced that they will remove the ability to use 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 in 2023. They're also disabling SMTP authentications in all tenants where it's currently not being used.

This change requires customers to migrate from/update from applications or services using basic authentication towards using Modern Authentication (OAuth 2.0 token-based authorization), more details can be found here:

https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/deprecation-of-basic-authentication-exchange-online

While Microsoft said that they are not making changes to SMTP AUTH, which is not in scope for this disablement now, we should consider adding support for OAUTH with SMTP Authentication in the future releases of RH-SSO (RHBK).