We are excited to announce support of Client Credential Flow (CCF) for SMTP AUTH in Exchange Online. CCF for SMTP AUTH allows applications to use Modern authentication for submitting authenticated emails to Exchange Online without the need for interactive sign-on. Using OAuth reduces the chances of credentials being compromised during authentication.
The key benefit of CCF for SMTP is that it allows non-interactive sign-ins using OAuth. Non-interactive sign-in means that applications, scripts, and other automation can benefit from the increased security of Modern auth.