Return-Path, Envelope From, etc.

[Roderick A. Anderson-4]

My understanding, from following several threads here and some research,
is the return-path is transmitted out-of-band in the SMTP MAIL request
and placed in the message by the LDA.

How would a proxy determine the value(s) that will be used to create the
Return-Path?

That make any sense?


TIA,
Rod
--

[Sahil Tandon]

On Nov 5, 2009, at 12:53 PM, "Roderick A. Anderson" <raanders@...
 > wrote:

> My understanding, from following several threads here and some  
> research, is the return-path is transmitted out-of-band in the SMTP  
> MAIL request and placed in the message by the LDA.
>
> How would a proxy determine the value(s) that will be used to create  
> the Return-Path?

Postfix sends the MAIL FROM (which it received from the original SMTP  
client) to the before queue proxy.  The MAIL FROM is used to construct  
the Return-Path: header.  There is only ONE Return-Path:.

[Victor Duchovni]

On Thu, Nov 05, 2009 at 09:53:51AM -0800, Roderick A. Anderson wrote:

> My understanding, from following several threads here and some research, is
> the return-path is transmitted out-of-band in the SMTP MAIL request and
> placed in the message by the LDA.

Yes, but not all LDAs add the header. It is optional.

"Out-of-band" means not in the message content (headers + body), but
in all other respects this is "in-band", as the envelope and message are
always transmitted together.

> How would a proxy determine the value(s) that will be used to create the
> Return-Path?

By looking at the envelope, e.g.

        MAIL FROM:<address> [ESMTP-parameter=value ...]

in the case of SMTP. Parsing the "MAIL FROM:" is a bit tricky given
addresses with quoted local parts.

    MAIL FROM:<"<annoying address form@...>"@example.com> SIZE=12345

so your lexical analysis needs to be able to handle this and similar
compexities from RFC 5321.

--
        Viktor.

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[Roderick A. Anderson-4]

Roderick A. Anderson wrote:
> My understanding, from following several threads here and some research,
> is the return-path is transmitted out-of-band in the SMTP MAIL request
> and placed in the message by the LDA.
>
> How would a proxy determine the value(s) that will be used to create the
> Return-Path?

Sahil, Victor;

Thank you for your quick responses.  You explanations make my
understanding more concise.

A little more reading about AMIL FROM on the Postfix site and I think
I'm on my way towards building the proxy I need.


Again thanks,
Rod
--

[Roderick A. Anderson-4]

Roderick A. Anderson wrote:

> Roderick A. Anderson wrote:
>> My understanding, from following several threads here and some
>> research, is the return-path is transmitted out-of-band in the SMTP
>> MAIL request and placed in the message by the LDA.
>>
>> How would a proxy determine the value(s) that will be used to create
>> the Return-Path?
>
> Sahil, Victor;
>
> Thank you for your quick responses.  You explanations make my
> understanding more concise.
>
> A little more reading about AMIL FROM on the Postfix site and I think
> I'm on my way towards building the proxy I need.

Besides the typo above (MAIL FROM) I forgot to ask is there an example
of how a message is formatted on it's way into the proxy?

I only need to look at the MAIL FROM, the message Subject header, and
possibly another message header.  Content isn't needed.


Again thanks,
Rod
--
>
>
> Again thanks,
> Rod

[Sahil Tandon]

On Nov 5, 2009, at 3:02 PM, "Roderick A. Anderson" <raanders@...
 > wrote:

> Roderick A. Anderson wrote:
>> Roderick A. Anderson wrote:
>>> My understanding, from following several threads here and some  
>>> research, is the return-path is transmitted out-of-band in the  
>>> SMTP MAIL request and placed in the message by the LDA.
>>>
>>> How would a proxy determine the value(s) that will be used to  
>>> create the Return-Path?
>> Sahil, Victor;
>> Thank you for your quick responses.  You explanations make my  
>> understanding more concise.
>> A little more reading about AMIL FROM on the Postfix site and I  
>> think I'm on my way towards building the proxy I need.
>
> Besides the typo above (MAIL FROM) I forgot to ask is there an  
> example of how a message is formatted on it's way into the proxy?
>
> I only need to look at the MAIL FROM, the message Subject header,  
> and possibly another message header.  Content isn't needed.

Postfix submits the message to the proxy via ESMTP.  See  
SMTPD_PROXY_README.

[mouss-4]

Roderick A. Anderson a écrit :

> Roderick A. Anderson wrote:
>> Roderick A. Anderson wrote:
>>> My understanding, from following several threads here and some
>>> research, is the return-path is transmitted out-of-band in the SMTP
>>> MAIL request and placed in the message by the LDA.
>>>
>>> How would a proxy determine the value(s) that will be used to create
>>> the Return-Path?
>>
>> Sahil, Victor;
>>
>> Thank you for your quick responses.  You explanations make my
>> understanding more concise.
>>
>> A little more reading about AMIL FROM on the Postfix site and I think
>> I'm on my way towards building the proxy I need.
>
> Besides the typo above (MAIL FROM) I forgot to ask is there an example
> of how a message is formatted on it's way into the proxy?
>
> I only need to look at the MAIL FROM, the message Subject header, and
> possibly another message header.  Content isn't needed.
>
>

you need to read about how SMTP works. it goes like this:

EHLO joe.example.com
...
MAIL FROM:<sender@...>
...
RCPT TO:<virginia@...>
...
DATA
...
header_1: value_1
header_2: value_2
...

body blah blah
.
QUIT



so the message (including the headers) is passed after the DATA command.
 the envelope sender is passed in the MAIL FROM: command. it may end up
ina Return-Path header, but as already said, this is config-dependent.