gnus-imap-message-count.el

(defun gnus-user-format-function-t (dummy)
  (case (car gnus-tmp-method)
    (nnimap
     (let ((count (nnimap-request-message-count gnus-tmp-qualified-group)))
       (if count
           (format "%d" count)
         "?")))
    (t
     gnus-tmp-number-total)))

(defvar nnimap-message-count-cache-alist nil)

(defun nnimap-message-count-cache-clear nil
  (setq nnimap-message-count-cache-alist nil))

(defun nnimap-message-count-cache-get (mbox &optional server)
  (when (nnimap-possibly-change-server server)
    (cadr (assoc (concat nnimap-current-server ":" mbox)
                 nnimap-message-count-cache-alist))))

(defun nnimap-message-count-cache-set (mbox count &optional server)
  (when (nnimap-possibly-change-server server)
    (push (list (concat nnimap-current-server ":" mbox)
                count) nnimap-message-count-cache-alist))
  count)



(defun nnimap-request-message-count (mbox &optional server)
  (let ((count (or (nnimap-message-count-cache-get mbox server)
                   (and (nnimap-possibly-change-server server)
                        (progn
                          (message "Requesting message count for %s..."
                                   mbox)
                          (prog1
                              (imap-mailbox-status
                               mbox 'messages nnimap-server-buffer)
                            (message "Requesting message count for %s...done"
                                     mbox)))))))
    (when count
      (nnimap-message-count-cache-set mbox count server))
    count))

(add-hook 'gnus-after-getting-new-news-hook 'nnimap-message-count-cache-clear)