Looks like GMail (or something else in the middle) indeed messes with
headers.

I get the correct headers in the messages received by a self-hosted Postfix:

List-Id: <caml-list.inria.fr>
List-Help: <mailto:sympa_inria@inria.fr?subject=help>
List-Subscribe: <mailto:sympa_inria@inria.fr?subject=subscribe%20caml-list>
List-Unsubscribe: <mailto:sympa_inria@inria.fr?subject=unsubscribe%20caml-list>
List-Post: <mailto:caml-list@inria.fr>
List-Owner: <mailto:caml-list-request@inria.fr>
List-Archive: <http://sympa.inria.fr/sympa/arc/caml-list>

However, Thunderbird doesn't seem to offer an unsubscribe option based on that header, and I can't remember any email client where I'd have seen that functionality.


On 1/5/21 2:42 AM, Yawar Amin wrote:
> Actually, this is puzzling indeed–I notice there's no
> 'List-Unsubscribe' header in the messages that reach my Gmail inbox,
> but it _is_ present in the message that gets archived at
> e.g. https://inbox.ocaml.org/caml-list/CAH=h3gEOoMUBezUb3NoXvksX34ke3etP8=aScYeCzRc9p-ehrg@mail.gmail.com/raw
> <https://inbox.ocaml.org/caml-list/CAH=h3gEOoMUBezUb3NoXvksX34ke3etP8=aScYeCzRc9p-ehrg@mail.gmail.com/raw>
>
>
> And in fact Gmail is not showing the 'unsubscribe' UI that it normally
> would if it found the 'List-Unsubscribe' header. Looks like something
> is stripping out the 'List-*' and perhaps other headers before
> delivering them to Gmail.
>
> Regards,
>
> Yawar