[RFCI-Discuss] qantas.com.au rejecting empty MAIL FROM:<> after RCPT TO and DSN list

[Andrew Buckeridge]

IronPort have a useless banner as with the malfeature in PrIX.
The munted banner and the response to HELP looks like Cico IronPort.
They don't accept bounces, but they defer until RCPT TO:<>.

Now an MTA could be clever and reject empty MAIL FROM:<> if the
RCPT TO:<> does not match one of their previous MAIL FROM:<>.
In such a case it could still be be accepting real DSNs.
If it doesn't then it need to be listed in DSN.

This will break SMTP callouts. To avoid backscatter bounces we
will have to proxy as message is received in real time.

> andrewb at thot:/tmp$ telnet mail1.qantas.com.au 25
> Trying 139.163.137.11...
> Connected to mail1.qantas.com.au.
> Escape character is '^]'.
> 220 mail1.qantas.com.au ESMTP
> ehlo n50.bgcaus.com
> 250-mail1.qantas.com.au
> 250-8BITMIME
> 250-SIZE 10485760
> 250 STARTTLS
> help
> 214-The following commands are recognized
> 214-    auth    data    ehlo    helo
> 214-    help    mail    noop    quit
> 214     rcpt    rset    starttls        vrfy
> help mail
> 214-The following commands are recognized
> 214-    auth    data    ehlo    helo
> 214-    help    mail    noop    quit
> 214     rcpt    rset    starttls        vrfy
> help rcpt
> 214-The following commands are recognized
> 214-    auth    data    ehlo    helo
> 214-    help    mail    noop    quit
> 214     rcpt    rset    starttls        vrfy
> 221 mail1.qantas.com.au
> Connection closed by foreign host.