[Mailman-Users] Explicit destination causes implicit destination bounce

Larry Stone lstone19 at stonejongleux.com
Fri Mar 11 19:04:12 CET 2011

On Fri, 11 Mar 2011, Ian Gibbs wrote:

> Dear all,
> I have read http://wiki.list.org/pages/viewpage.action?pageId=4030676 FAQ 1.9 
> about implicit destination. I am sending directly To: the list with no other 
> recipients. The host_name setting is pumb.org.uk. The conversation I had with 
> the SMTP server is shown below. It still results in an implicit destination 
> error. Can anyone suggest why, please?

You have no To: header (or any other headers for that matter). The 
recipient listed on a RCPT TO: command to the SMTP server (known in the 
SMTP world as the "envelope recipient") is not the same as a To: header. 
Since the Mailman list address was not found in the message's non-existent 
To: or Cc: headers, it is an implicit destination.

To SMTP, headers are part of the message's data. They are completely 
separate from the SMTP commands that tell an SMTP server what to do with 
the message (otherwise, BCC could not work. A BCC recipient never appears 
in the headers (or wouldn't be blind) but the BCC recipient must be in the 
RCPT TO: SMTP command as how else would the destination server know to 
deliver it to the BCC recipient).

> user at workstation:~$ telnet server 25
> Trying IP...
> Connected to server.
> Escape character is '^]'. 
> 220 server ESMTP Exim 4.71 Fri, 11 Mar 2011 14:43:29 +0000
> HELO workstation
> 250 server Hello workstation []
> MAIL FROM:external at email.address 
> 250 OK
> RCPT TO:mailman at pumb.org.uk
> 250 Accepted
> 354 Enter message, ending with "." on a line by itself
> Subject:Testing from guinevere 3
> This is a message 3
> .
> 250 OK id=1Py3ZU-0003YI-Rz
> 221 server closing connection
> Connection closed by foreign host.

-- Larry Stone
    lstone19 at stonejongleux.com

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