Variable: nnmail-keep-last-article
nnmail-keep-last-article is a customizable variable defined in
nnmail.el.gz.
Value
nil
Documentation
If non-nil, nnmail will never delete/move a group's last article.
It can be marked expirable, so it will be deleted when it is no longer last.
You may need to set this variable if other programs are putting new mail into folder numbers that Gnus has marked as expired.
Source Code
;; Defined in /usr/src/emacs/lisp/gnus/nnmail.el.gz
;; Added by gord@enci.ucalgary.ca (Gordon Matzigkeit).
(defcustom nnmail-keep-last-article nil
"If non-nil, nnmail will never delete/move a group's last article.
It can be marked expirable, so it will be deleted when it is no longer last.
You may need to set this variable if other programs are putting
new mail into folder numbers that Gnus has marked as expired."
:group 'nnmail-procmail
:group 'nnmail-various
:type 'boolean)