FYI, the entire email error message below
The original message was received at Tue, 2 Mar 2021 12:53:52 -0800
from m0144480.ppops.net [127.0.0.1]
----- The following addresses had permanent fatal errors -----
<noreply@malwarebytes.com>
(reason: 554 5.4.14 Hop count exceeded - possible mail loop ATTR34 [SN1NAM04FT005.eop-NAM04.prod.protection.outlook.com])
----- Transcript of session follows -----
... while talking to malwarebytes-com.mail.protection.outlook.com.:
>>> DATA
<<< 554 5.4.14 Hop count exceeded - possible mail loop ATTR34 [SN1NAM04FT005.eop-NAM04.prod.protection.outlook.com]
554 5.0.0 Service unavailable