@Tomas Hajny
Ah - thank you. Very strange. I did not expect and did not notice that when I click on "reply to list", the reply uses another mail address than the one the mail was sent to.
Looks like an error of the thunderbird mailprogramm, I think replies should always use the same mail address that the incoming mail used. Anyway, I will try to take care that in the future I send my replies to the list from my registered address.
Franz
