The original message was received at Mon, 20 Nov 2023 17:03:54 -0500 from m0338037.ppops.net [127.0.0.1] ----- The following addresses had permanent fatal errors ----- <frank_neffke@hks.harvard.edu> (reason: 554 5.4.14 Hop count exceeded - possible mail loop ATTR34 [SN1PEPF000252A4.namprd05.prod.outlook.com 2023-11-20T22:03:55.247Z 08DBE74DB4CEB715]) ----- Transcript of session follows ----- ... while talking to hu.mail.protection.outlook.com.:

...

...

DATA <<< 554 5.4.14 Hop count exceeded - possible mail loop ATTR34 [SN1PEPF000252A4.namprd05.prod.outlook.com 2023-11-20T22:03:55.247Z 08DBE74DB4CEB715] 554 5.0.0 Service unavailable