[Mailman-Users] short question, probably an FAQ that I've overlooked.

Larry Stone lstone19 at stonejongleux.com
Fri Jun 3 03:22:47 CEST 2005

On 6/2/05 7:57 PM, Brad Knowles at brad at stop.mail-abuse.org wrote:

> At 7:50 PM -0500 2005-06-02, Larry Stone wrote:
>>  Brad, I realize this is getting a little off of Mailman but how is that
>>  different from what a BCC does? A BCC "header" is local to the originating
>>  MUA - it doesn't appear in the transmitted message but the BCC recipients do
>>  become envelope recipients. So from the view of the MTA, isn't what you say
>>  Mailman does exactly the same as what the MUA does with a BCC?
> Well, "Bcc:" is a header.  Mailman never uses a "Bcc:" header.
> In terms of the implementation, by listing multiple envelope
> recipients, there is no practical difference.

> The technical difference is that a "Bcc:" header is something
> that would typically be added by an MUA, but an MUA wouldn't know
> enough about the SMTP protocol in order to be able to provide
> multiple envelope recipients directly.  In this case, it's up to the
> MTA to take the "Bcc:" header and interpret those contents
> appropriately.

Wow. I thought I knew how an MUA and an MTA interfaced. But what you're
saying is that an MUA can send the MTA a BCC header (which, of course, is in
the DATA section of the SMTP exchange) and rely on the MTA to strip out the
BCC and add the additional envelope recipients.
> However, Mailman does know enough about the SMTP protocol that it
> can by-pass the use of a "Bcc:" header, and go straight to listing
> multiple envelope recipients.

Considering that every MUA I use can communicate with the MTA via the SMTP
port, I assumed (assumed - that's dangerous) that it was sending normal SMTP
commands - i.e. a MAIL FROM command, one or more RCPT TO commands, and a
DATA command followed by the message. And I assumed (there's that word
again) that the MTA did nothing with the To and Cc headers other than to
pass them on unchanged. So is there something different going on between an
MUA and an MTA? Or if not, why would an MUA not know enough about SMTP to
send multiple envelope recipients.

-- Larry Stone
   lstone19 at stonejongleux.com

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