Is not authorized to relay messages

[sainath]

Hi Team,

I am using Zimbra Collaboration 8.8.8.GA.2009 Open Source Software for Mailing solution. My Mail server is working perfectly for all other domains and I had also created all DNS Records correctly. But when I am trying to send a mail to Payu.com domain I will get an error.
From many days I am facing this issue with one of the Office 365 Domain which I am unable to send messages to payu.com domain. When I am sending the mail to payu.com domain I am getting below error saying
"Your message to team@payu.com couldn't be delivered.
sainath is not authorized to relay messages through the server that reported this error."

Sometimes I will also get the different error

"Your message:
From: sainath@medeaz.com
Subject: Test Mail

Could not be delivered because of

Server refused mail at END OF DATA - 554 5.4.14 Hop count exceeded - possible mail loop ATTR34 [VE1EUR02FT057.eop-EUR02.prod.protection.outlook.com]

The following recipients were affected:
team@payu.com"

Would someone help me in resolving this issue. Its a payment gateway so, I need to get a solution for this on priority. Thank you in advance.

If you need any additional information. Please let me know.

Regards
Sainath

[sainath]

Would someone please help on this issue and suggest me the how to resolve the issue.

[DavidMerrill]

"Hop count exceeded - possible mail loop" is telling. Chase this down, a mail loop is happening for a reason. Troll the logs, can you see the mail loop happening?