Description of problem: Office365 is now enabling the XOAUTH2 authentication method and on RHEL 8 it seems that there is no possibility to configure sendmail to make use of that new authentication method. Version-Release number of selected component (if applicable): sendmail-8.15.2-34 How reproducible: Always
I think it's similar as with postfix. You need cyrus-sasl xoauth plugin which AFAIK is not yet in RHEL.