How do I set a DKIM header in Thunderbird?
I have set up a DKIM record in the DNS for my domain and want to send all emails from Thunderbird with the matching header in it... but I can't find anywhere in Thunderbird where I can set that and there is nothing in the Thunderbird help about it... that I can find, anyway.
Alla svar (1)
You are looking for something which does not exist. DKIM is added by the mail server, not the client.
Hopefully you can find your server software listed here http://www.dkim.org/deploy/index.html