On 20/03/2020 19:49, Martin Gregorie wrote:
> On Fri, 20 Mar 2020 13:03:53 +0000, The Natural Philosopher wrote:
>
>> On 20/03/2020 12:43, Martin Gregorie wrote:
>>> On Fri, 20 Mar 2020 10:47:38 +0000, The Natural Philosopher wrote:
>>>
>>>> On 20/03/2020 10:02, Martin Gregorie wrote:
>>>>> Its well-known that the From: header is not used at all to transfer
>>>>> mail from sender to receiver - returned bounces are sent to the
>>>>> Reply-To address.
>>>> No, to the envelope from address.
>>>>
>>> Regardless, the point I was trying to make is that the From: header is
>>> not used by the process of transferring mail from sender to recipient
>>> and is displayed by the receiving MUA for information only.
>>>
>>> So it can be, and is, used nefariously by spammers and other lowlife.
>>>
>>>
>> No, the From: address is simply a header until you try and respond to an
>> email, when it is, after 'reply to:', the default recipient (long with
>> any cc: lists.
>>
> The fact that you can reply to it only occurs because your MUA displayed
> it in such a way that you can reply to it. It can be plain wrong: how
> many times have you seen a sender displayed by your MUA as:
>
>  From [Close Friend ]
>
> You haven't? Then one of the following applies
> (a) your MUA isn't configured to show the address after the display-name
> (b) your MUA can't/won't show the from address, so ditch it and get a
>      better one
> (c) you haven't been watching out for spam
>
>
>> So it is not just displayed for information.
>>
>> For clarity, the SMTP protocol is:
>> Helo  (can be anything)
>> Mail From 
>>
> envelope sender is NOT the From: header and nothing says that there has
> to be a From: header or that irs content has to be the same as the
> envelope-from content
I never said it was.

The mail From sequence in smtp has nothing to do with the From: header
>
> Same goes for the Return-address: and Reply-To: addresses though, because
> they are automatically set from the sender's account name and server
> domain, they are more likely to be correct.

They are not,. Reply-to: is set by the senders MUA itself

Return-address: is a new feature that is set to the envelope from.
>
>> RCPT to 
>> data which is where the headers are sent, followed by the message parts.
>>
>> That is, the SMTP exchange has nothing to do with the headers BUT once
>> delivered, the headers are what the MUA uses to respond
>
>


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