Here's a site that 1) tells other sites to send mail via MAILER,
2) doesn't have MAILER!!!, 3) bounces mail to From:, not Sender:.
 
Dimitri Vulis
 
Received: From CUDENVER(POSTMAST) by CUNYVMS1 with Jnet id 8485
          for DLV@CUNYVMS1; Sat, 15 Sep 90 17:00 EDT
Date:     Sat, 15 Sep 90 14:59 MDT
From:     <POSTMASTER@CUDENVER>
Subject:  Returned Network Mail
To:       DLV@CUNYVMS1
Original_To:  BITNET%"[log in to unmask]"
 
 
Your mail is being returned to you.
Reason for return is:
%MAIL-E-NOSUCHUSR, no such user MAILER at node CUDNVR
Returned mail follows:
------------------------------
Received: From UCBCMSA(MAILER) by CUDENVER with Jnet id 3023
          for MAILER@CUDENVER; Sat, 15 Sep 90 14:59 MDT
HELO UCBCMSA.BITNET
TICK 3791
MAIL FROM:<[log in to unmask]>
RCPT TO:<[log in to unmask]>
DATA
Received: by UCBCMSA (Mailer R2.04) id 3791; Sat, 15 Sep 90 13:56:10 PDT
Date:         Sat, 15 Sep 90 16:18:00 EDT
Sender:       Soviet Union to EARN Connections Technical Discussion
              <[log in to unmask]>
From:         Dimitri Vulis <[log in to unmask]>
Subject:      .SU
To:           Lloyd Brodsky <[log in to unmask]>
 
[message deleted]
Dimitri
.
QUIT