Issue realted sending message for some mailboxs from on premise and exchange online

Dear elnadey,

Good day!

Thank you for posting to Microsoft Community. We are glad to assist!

Based on your description regarding "Issue related sending message for some mailboxs from on premise and exchange online".Kindly check this article 554 5.4.14 Hop count exceeded - possible mail loop NDR for outgoing email - Exchange | Microsoft Learn if it can provide any suitable information about your mentioned issue concern.

If the issue persists, I therefore believe that this issue should be further investigated by our online technical support team. A support Engineer can further connect with you remotely, for further troubleshooting and involve the backend team where need be. The team might request for your public IP address or collect certain detailed logs information with more technical resources. Please understand that as public forum support, we don’t have higher permissions to check and analyze these logs or check the IP addresses and considering your scenario maybe inconveniencing, to quickly help assist, kindly contact your organization admin or you can create a service request to report this symptom to our online channel. Here is contact support document: Get support - Microsoft 365 admin | Microsoft Learn

Important Note: If any organization's Office 365 Business / Enterprise subscription is from syndicate or reseller partner and if global admin cannot open service request from their side, they may need to contact reseller support provider so that they can help to global admin for opening service request from their side, after that Office 365 technical support team can involve in service request. Thanks for your precious time and your understanding would be highly appreciated. Have a nice day!

Best regards,

Inema |Community Moderator

thanks your response

i already see that topic

But i don't have edge server

i have exchange 2016 and exchange online hybrid and domain name is : ABC.com for both

and mailbox on premise when sent message to online mailbox not delivery and when check messages trace

Error: ‎554 5.4.14 Hop count exceeded - possible mail loop ATTR34 [DBB.eurprd03.prod.outlook.com 2024-04-29T08:53:47.871Z 082511F4B]‎

also there is no any application

i need to solve it

thanks