I had noticed that email to one of our RT instances was hanging around
in the queue with a EX_TEMPFAIL error code.
I made up a dummy test message and performed:
cat /tmp/x | /etc/smrsh/rt-mailgate --queue support --action correspond
–url https://our.internal.url/rt3
And it returned:
An Error Occurred
404 Not Found
What in the heck does that mean? Since it is so late, my mind is a bit
mushy… 
-Rich
