"Resent-" headers

Is there something special about "Resent-" headers?

I have a recipe that forwards a copy of some messages to another user.
But sometimes the message doesn't get delivered - and the procmail log file
doesn't report an error.

This is the simple recipe I use to email a copy:

   # for this example
   COPYTO=moseley(_at_)netcom(_dot_)com


   # if COPYTO is defined then send a copy

   :0c
   * COPYTO ?? .
   | formail -i"From: (Copy) $FROM" \
             -i"Reply-To: $FROM" \
             -I"To: $COPYTO" \
             -A"X-Loop: moseley(_at_)netcom(_dot_)com"  | $SENDMAIL -oi -t


To try to find the problem, I grabbed a procmail list message from today
because procmail list messages contain a lot of headers and I suspected that
to be the problem.  I piped it into sendmail to try to test it.
For testing I used:

   cat msg | /usr/lib/sendmail -t

where msg contained the mail message.

sendmail would run and no error messages were displayed.  But the mail would
vanish, never to be seen again (yet?).

Finally, to get the mail to deliver I found that I had to do either:

 - delete all the headers that started with "Resent-"

 - or send the message like this:

   cat msg | /usr/lib/sendmail moseley(_at_)netcom(_dot_)com(_dot_)

and the "Resent-" headers get passed along fine.


Can anyone explain why deleting the "Resent-" headers made sendmail happy
and willing to deliver the message?

And why passing an email address in the sendmail command line worked without
having to delete the Resent- headers?

And what happened to the messages that sendmail accepted but didn't delete?
Where are they?

Did this type of mystery bother you too when you were first learning?

Thanks,

Bill
moseley(_at_)netcom(_dot_)com