I had a problem something like this quite a while ago. I
          discovered that it arose as follows:
 
          A site running a small DECNET net had written a gateway to
          Bitnet for the convenience of the technical support group
          there. It emitted messages from the "Postmaster" address.
          General users weren't supposed to know about the gateway,
          but at least one did....
 
          _Maybe_ your bounced mail arises from this cause. If so, the
          best thing to do is contact the Postmaster right away....
 
          Cheers, Nollaig
          --------------------------------------------------
          --------------------------------------------------
Hi there,
  Several of our local lists have recently started bouncing messages
from userid's like: [log in to unmask]  The stated reason is usually
"mail origin seems to be a mailer or mail-daemon."
 
This is the header of one offending posting:
>Date:     Tue,  6 Aug 1991 16:52 EDT
>Original_From:  NEIS::ALERT
>Comments: This is gatewayed mail.  Warning:  Mail may not
>          necessarily be returnable through this path.
>From:     General Delivery <POSTMASTER@USGSRESV>
>To:       SEISM-L@BINGVMB
>Original_To:  ISDRES::BITNET%"SEISM-L@BINGVM
 
                ....................
.....................  Some gateways (only on VAX/VMS machines so
far) make outgoing mail appear to listserv to be from the userid POSTMASTER.