Date: Wed, 12 Sep 2001 09:51:40 +0100 From: Ceri <ceri@techsupport.co.uk> To: Duke Normandin <01031149@3web.net> Cc: Freebsd Questions <freebsd-questions@freebsd.org> Subject: Re: Why, this is new (and BAD, BAD, BAD!!) ... Message-ID: <20010912095140.C19861@cartman.private.techsupport.co.uk> In-Reply-To: <20010911192321.B256075@mandy.rockingd.calgary.ab.ca>; from 01031149@3web.net on Tue, Sep 11, 2001 at 07:23:21PM -0600 References: <20010911154213.A22243@router.darlow.co.uk> <20010911192321.B256075@mandy.rockingd.calgary.ab.ca>
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On Tue, Sep 11, 2001 at 07:23:21PM -0600, Duke Normandin said:
>
> In an effort to flesh out my understanding of the inner workings of email
> in general, could you please define exactly what is meant by "envelope"?
> Please use the headers that will accompany your reply as an example, so
> that I can *see* it, and differentiate it from the other headers. TIA...
Best way to explain this is with a sample SMTP session, I feel.
---begin
setantae@shaft setantae$ telnet 0 smtp
Trying 0.0.0.0...
Connected to 0.
Escape character is '^]'.
220 shaft.techsupport.co.uk ESMTP Exim 3.22 #1 Wed, 12 Sep 2001 09:43:11 +0100
helo shaft.techsupport.co.uk
250 shaft.techsupport.co.uk Hello shaft.techsupport.co.uk [212.250.77.214]
mail from: <ceri@techsupport.co.uk>
250 <ceri@techsupport.co.uk> is syntactically correct
rcpt to: <setantae@submonkey.net>
250 <setantae@submonkey.net> is syntactically correct
rcpt to: <someoneyoudontknowabout@example.com>
250 <someoneyoudontknowabout@example.com> is syntactically correct
data
354 Enter message, ending with "." on a line by itself
From: "Ceri" <ceri@techsupport.co.uk>
To: "MadeUp Name" <john@example.com>
Subject: bar
This is a test.
.
250 OK id=15h5cB-0006RI-00
quit
221 shaft.techsupport.co.uk closing connection
Connection closed by foreign host.
---end
The ``mail from:'' and ``rcpt to:'' lines are the envelope, basically.
The actual headers sent after the ``data'' command may or may not give the
same information, the difference being that only the envelope determines
where the message actually gets delivered.
A bounce message gets delivered to the sender as specified in the envelope,
but most MUAs will show you the sender according to the headers in the
``data'' portion.
Also note that an additional recipient was specified in the envelope, but
not in the ``data'' portion - this is how BCC is implemented.
Here is the message I received at the setantae@submonkey.net address,
with headers.
---begin
From ceri@techsupport.co.uk Wed Sep 12 09:42:23 2001
Return-path: <ceri@techsupport.co.uk>
Envelope-to: ceri@localhost
Delivery-date: Wed, 12 Sep 2001 09:42:23 +0100
Received: from localhost ([127.0.0.1])
by cartman.private.techsupport.co.uk with esmtp (Exim 3.31 #1)
id 15h5bD-0005Th-00
for ceri@localhost; Wed, 12 Sep 2001 09:42:23 +0100
Delivered-To: setantae@eidosnet.co.uk
Received: from mail.eidosnet.co.uk [195.40.67.19]
by localhost with POP3 (fetchmail-5.7.4)
for ceri@localhost (single-drop); Wed, 12 Sep 2001 09:42:23 +0100 (BST)
Received: (qmail 91382 invoked from network); 12 Sep 2001 08:42:00 -0000
Received: from mars.easily.co.uk ([213.219.14.243]) (envelope-sender <ceri@techsupport.co.uk>)
by nectarine.mail.uk.easynet.net (qmail-ldap-1.03) with SMTP
for <setantae@eidosnet.co.uk>; 12 Sep 2001 08:42:00 -0000
Received: from shaft.techsupport.co.uk (shaft.techsupport.co.uk [212.250.77.214])
by mars.easily.co.uk (Postfix) with ESMTP id 6C859120B9
for <setantae@submonkey.net>; Wed, 12 Sep 2001 09:41:55 +0100 (BST)
Received: from shaft.techsupport.co.uk ([212.250.77.214])
by shaft.techsupport.co.uk with smtp (Exim 3.22 #1)
id 15h5cB-0006RI-00
for setantae@submonkey.net; Wed, 12 Sep 2001 09:43:50 +0100
From: "Ceri" <ceri@techsupport.co.uk>
To: "MadeUp Name" <john@example.com>
Subject: bar
Message-Id: <E15h5cB-0006RI-00@shaft.techsupport.co.uk>
Date: Wed, 12 Sep 2001 09:43:50 +0100
This is a test.
---end
Now while the headers are a tad confusing due to my use of .forwards and
fetchmail for the submonkey.net address, note how the only mention of
setantae@submonkey.net address is in the Received headers - this is because
it's the envelope address.
The To: address is just something I invented.
Hopefully that makes some kind of sense - it's easy to understand but hard
(for me) to explain.
Google is failing to turn up any _good_ explanations, but the best one I've
seen is in Philip Hazel's Exim book (although I haven't read it all - it
looked good during the glance I took at it).
Ceri
--
Your local RFC Nazi
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