The original message was received at Fri, 16 Feb 2024 04:20:00 -0500 from m0172791.ppops.net [127.0.0.1] ----- The following addresses had permanent fatal errors ----- <xiaonw@wharton.upenn.edu> (reason: 554 5.4.14 Hop count exceeded - possible mail loop ATTR34 [BL6PEPF0001AB4D.namprd04.prod.outlook.com 2024-02-16T09:20:01.389Z 08DC2C409A20DF62]) ----- Transcript of session follows ----- ... while talking to penno365-mail-onmicrosoft-com.mail.protection.outlook.com.:

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DATA <<< 554 5.4.14 Hop count exceeded - possible mail loop ATTR34 [BL6PEPF0001AB4D.namprd04.prod.outlook.com 2024-02-16T09:20:01.389Z 08DC2C409A20DF62] 554 5.0.0 Service unavailable