exchange NDR error 5.3.5

[NATCAT]

Hi all,

Periodically I'm getting the NDR message below. There is no similarity with time or recipient domiain. Everything seems to be working fine although I'm getting these error more frequently. We have a backend and front end exchange servers.

The following recipient(s) could not be reached:

[Recipient name] on 4/10/2006 6:15 AM
A configuration error in the e-mail system caused the message to bounce between two servers or to be forwarded between two recipients. Contact your administrator.
<[internal exchange server] #5.3.5>

There is no information in the event logs pointing to this problem on either the front end or backend server

Can anyone help me being to troubleshoot ?

 

[NATCAT]

PS: I was able to send email to the same recipient 2 hours after I got this NDR.

 

[NATCAT]

I've changed the SMTP connector for the backend server to point to the frontend server instead of pointing to itself like it was before.

But I still don't understand why that setup was only occasionally giving problems.

Even though I belive the problem is solved does anyone have any possible explainations as to why SOME users were recieving an NDR SOME of the time ?