The original message was received at Fri, 1 Sep 2023 04:28:38 -0400 from m0338035.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 [BN7NAM10FT099.eop-nam10.prod.protection.outlook.com 2023-09-01T08:28:39.448Z 08DBA9D9869850A1]) ----- Transcript of session follows ----- ... while talking to hu.mail.protection.outlook.com.:

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DATA <<< 554 5.4.14 Hop count exceeded - possible mail loop ATTR34 [BN7NAM10FT099.eop-nam10.prod.protection.outlook.com 2023-09-01T08:28:39.448Z 08DBA9D9869850A1] 554 5.0.0 Service unavailable