The mailing list for listmasters using Sympa

[David Carter <address@concealed>]

On 2021-01-11 05:05, Youcef N Baouchi wrote:
> Hi Soji,
>
> A screenshot is attached. For some reason the -request address
> sometimes gets cached which causes people to email -request alias
> instead of the actual list. But when I look at the headers the
> -request address is in the sender field not the from field.

Given:

 From: <email>
 Sender: address@concealed

Outlook will display:

 address@concealed on behalf of <email>

This has always been Microsoft's interpretation of 
https://tools.ietf.org/html/rfc5322 :

   3.6.2.  Originator Fields

   ...

   The originator fields indicate the mailbox(es) of the source of the
   message.  The "From:" field specifies the author(s) of the message,
   that is, the mailbox(es) of the person(s) or system(s) responsible
   for the writing of the message.  The "Sender:" field specifies the
   mailbox of the agent responsible for the actual transmission of the
   message.  For example, if a secretary were to send a message for
   another person, the mailbox of the secretary would appear in the
   "Sender:" field and the mailbox of the actual author would appear in
   the "From:" field.  If the originator of the message can be indicated
   by a single mailbox and the author and transmitter are identical, the
   "Sender:" field SHOULD NOT be used.  Otherwise, both fields SHOULD
   appear.

It looks like they focused on the bit which reads "if a secretary were 
to send a message for another person".

Sympa isn't doing anything wrong: other Mailing List Managers also add 
Sender: headers.

I guess there is an argument for not adding a Sender: header given that 
the last sentence is a SHOULD rather than a MUST.