Composite Authentication Question

[omarion]

All,

I sent a test email to myself in my Office 365 Work Email Box. I look at the headers and discover my compauth=other with reason=501. What does this mean?

[#2]

You can read about Composite authentication here:  https://docs.microsoft.com/en-us/office365/securitycompliance/anti-spoofing-protection#composite-aut...

[#3]

Neither that page nor the "Anti-spam message headers in Microsoft 365" page that it references says anything about compauth=other nor reason=501.