The maximum hop count was exceeded for this message. This non-delivery report can also be caused if a looping condition exists between sending and receiving servers that are not in the same Exchange organization. In this situation, the message bounces back and forth until the hop count is exceeded. A configuration error in the e-mail system can also cause the message to bounce between two servers or to be forwarded between two recipients.
The maximum hop count is a property set on each virtual server and you can manually override it. The default maximum hop count is 15. Also, check for any situations that might cause loops between servers