The original message was received at Fri, 16 Feb 2024 04:18:09 -0500 from m0338036.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 [DS2PEPF00003447.namprd04.prod.outlook.com 2024-02-16T09:18:10.604Z 08DC2C5116D6B3E1]) ----- Transcript of session follows ----- ... while talking to hu.mail.protection.outlook.com.:

...

...

DATA <<< 554 5.4.14 Hop count exceeded - possible mail loop ATTR34 [DS2PEPF00003447.namprd04.prod.outlook.com 2024-02-16T09:18:10.604Z 08DC2C5116D6B3E1] 554 5.0.0 Service unavailable