The mailing list for listmasters using Sympa

[IKEDA Soji <address@concealed>]

> 2021/01/11 17:47、David Carter <address@concealed>のメール:
> 
> On 2021-01-11 08:00, IKEDA Soji wrote:
> 
>> It is a discussion that has repeated many times in anywhere dealing
>> with mailing list system.  However, removing “Sender:” field with
>> list’s address, instead of originator’s address, will prevent
>> delivering any messages sanely via mailing lists among the Internet.
> 
> The envelope sender / Return-Path: / SMTP MAIL FROM obviously has to be 
> address@concealed to collect bounces.
> 
> I'm curious why the Sender: header in the message body also needs to be 
> set. Two potential reasons come to mind:
> 
> 1) Broken MTAs which replace the envelope sender with the body Sender:
> 2) Protection again mail loops.
> 
> I'm willing to believe that I'm missing something really obvious here, 
> having never tried to remove the Sender: header myself.

It’s used for domain authentication of message sender.  As some services like 
mailng list manager rewrite envelope sender — at the first place, it’s domain 
is not always the same as one of originator’s address — “Sender:” field was 
used to keep the domain to be authorized by receiver.  An example is Sender 
ID.

Now “authentication” methods as above are considered historic.  However, 
while not all mail servers have adopted more reliable domain authentication 
mechanisms (e.g. a combination of DKIM and ARC for mailing lists), we cannot 
throw this old method away.

> 
> When my users ask, I just tell them that Microsoft are "special". 
> Unfortunately it is becoming more obvious these days as we migrate to 
> Microsoft 365.

I agree.


Regards,
— Soji