Implement Support for OAuth 2.0 to Replace Basic SMTP

We are sending emails from our internal domain. To secure communications and systems, it would be ideal to implement support for OAuth 2.0 for emails to authenticate, rather than using basic SMTP.

Microsoft identity platform and OAuth 2.0 authorization code flow - Microsoft identity platform | Microsoft Learn

I have looked into Azure Email Communication Services, however, this costs additionally per email and per size of email and adds an additional layer of complexity.