Answer
GMS has detected that this message has been sent between servers too many times and is probably in a loop. Therefore the attempt to deliver the message has been rejected and the message returned to sender. GMS saves resources by carrying out this check once per email message (and not for each recipient of the email message).
In this case, session Undefined was processing a message from the server at Undefined apparently from Undefined. The message has been rejected with
Undefined
To solve this problem check the resolution of the domain name goes to the right IP address and that the server at that IP address has been configured to accept the email message. You may need to inform the owner of the system at Undefined if their system is configured incorrectly.
Checking the contents of the email message should indicate how many mail servers are in the loop. To increase the maximum number of allowed loops, change the global value "MaxHopCount". In general the default value of 17 is high enough.
See Also:
Keywords:hop count MaxHopCount exceed rejected loop