>>> "AS" == Andreas Schwab <schwab@linux-m68k.org> writes:

> On Feb 11 2019, Adam Sjøgren <asjo@koldfront.dk> wrote:
>> It worked when I tried, as I showed.

> It works for me when sent through my primary MTA, but not when sent
> through an alternative MTA.  Either it depends on the MTA, or
> sendmail/postfix handles it correctly, but smtpmail-send-it doesn't.

Thunderbird/Seamonkey does not support it neither.