gnus-message-archive-group

gnus-message-archive-group is a variable defined in `gnus.el'.
Its value is

((format-time-string "sent.%Y-%m"))

Documentation:
*Name of the group in which to save the messages you've written.
This can either be a string; a list of strings; or an alist
of regexps/functions/forms to be evaluated to return a string (or a list
of strings). The functions are called with the name of the current
group (or nil) as a parameter.

If you want to save your mail in one group and the news articles you
write in another group, you could say something like:

(setq gnus-message-archive-group
'((if (message-news-p)
"misc-news"
"misc-mail")))

Normally the group names returned by this variable should be
unprefixed -- which implicitly means "store on the archive server".
However, you may wish to store the message on some other server. In
that case, just return a fully prefixed name of the group --
"nnml+private:mail.misc", for instance.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.1 of Emacs.