Emanuel Berg <embe8573@student.uu.se> writes:

> When I answer a mail in Gnus (with
> `gnus-article-followup-with-original') I get an
> undesired Cc header (with my own mail address).

Try to check message-default-mail-headers variable. Maybe you should
unset it?

> I suppose this is some hack to get a "sent messages" archive (?)

Hm... How have you done such an interesting conclusion? Certainly
no. Because the mail copy should pass an external mail server and return
again, but you could put it into archive just *before* sending, so why
do you need to wait its returning?

It's a feature, that provide users of some ugly smtp services like GMail
for getting they mails from mailing lists, because GMail drops them as
duplicates.