[LINK] Question re mail addressing

[Craig Sanders]

On Sat, Feb 03, 2007 at 07:38:31AM +1100, rchirgwin at ozemail.com.au wrote:
> So the question is: how can the message arrive at my inbox if it doesn't 
> have my address in the To: field? A mail server so badly configured that 
> it delivers stuff to "nearby" addresses is hard to credit, so I am 
> assuming that the spammer is obfuscating the To: field - is that possible?

it's much simpler than that.

"To:" fields, like *ALL* header fields are mere comments. they are NOT
addressing information, they do not control delivery. they can contain
anything, or nothing, or completely made up bogus rubbish.

the addressing data is in the email envelope, not in the headers. this
is transmitted during the SMTP session negotiation, "HELO" or "EHLO"
to establish mailer capabilities, followed by "MAIL FROM:<address>",
followed by one or more "RCPT TO:<address>" lines. finally, the message
data (including headers and body) are sent.

(actually, SMTP isn't the only mail transport protocol, just the most
common. other protocols, like uucp, have their own methods of doing
the same thing - the msg envelope specifies address, headers are only
data/comments just like the msg body)


now, it might *seem* like headers are used for addressing, but that's
only because mail clients commonly take the To: header and use it to
construct the envelope recipient address when sending a message. but
mail software, including spamware, doesn't have to do that - it can
completely ignore the To: header and make up whatever it likes for the
envelope To: address.

mailing lists, for example, do that all the time. examine the To: header
on your mailing list mail - LINK, for example. the To: header will say
something like:

   To: link at anu.edu.au

but it will be delivered to you.

craig

ps: this issue causes a fair amount of confusion for newbies on
mail-server support lists/forums - the distinction between envelope and
headers is an important one to understand for mail users/admins.


-- 
craig sanders <cas at taz.net.au>

Currently listening to: Tristan Boyle - Latent Belated Psychedelic Mayhem

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