Since it is almost inevitable that this will happen I would try the following:

put something like this in your rules.mer file

If not header "F" contains "postmaster@targetserver.com" SkipNext ""

If header "T" contains "source@sourceserver.com" SendMessage "source@sourceserver.com:error.txt"

If not header "F" contains "postmaster@targetserver.com" SkipNext ""
If header "T" contains "source@sourceserver.com" Delete ""

you would have to create the file error.txt  with the message you want it to say

An email that was just auto-forwarded to target@targetserver.com was not delivered.  It was probably too big.

I think that will work, perhaps others can expand on my idea.

Dear Gurus,

I found a serious problem in my Mercury setup. If I setup a auto forward in Mercury, e.g. all incoming emails of source@sourceserver.com will be forwarded to target@targetserver.com. If the mail cannot deliver to the target@targetserver.com (e.g. exceed the size limit), targetserver will send back an undeliverable notice with the original email to source@sourceserver.com and this notice will forward to target@targetserver.com again. This create a non-stop forward and backward loop between source@sourceserver.com and target@targetserver.com.

Did I setup my Mercury32 incorrectly or it behaves in this way originally? Is there any way to fix it?

Thanks.

Isaac

On the target do you include the whole forwarded message in the error message? In that case the forward would result in new error message every roundtrip and thus no chance for the involved servers to recognize it is a roundtrip. In that case reduce the citation in the errormessage to reasonable headerlines.

The simple solution may be to egalize the size-limit of the involved servers.

bye   Olaf