Gnus: IMAP-related questions

[thorsopia]

Hi,

I have several questions connected with IMAP.

I decided to post them in a single thread because I don't want to
overwhelm the list.

Server's "~/.gnus.el":

(add-to-list 'gnus-secondary-select-methods '(nnml ""))
(eval-after-load "mail-source"
  '(add-to-list 'mail-sources '(maildir :path "~/Maildir/"
                                        :subdirs ("cur" "new"))))

Client's "~/.gnus.el":

(setq mail-sources '((imap :server "mail.example.com"
                                                   :port 993
                                                   :stream ssl
                                                   :dontexpunge nil)))

1. How to verify server's certificate? (Will the same work for SMTP?)

2. ":dontexpunge nil" doesn't delete messages from the server. Why?
   (I checked via server's Gnus.)

3. "Group" buffer always says "No more unread newsgroups". But I'll
   see new emails if I hit "A A" in the "Group" buffer. Should I fix
   this? (How?)

4. I marked some messages with "E", quit the "Group" buffer with "q",
   quit Gnus with "q". Then I reopened Gnus and "E" marks
   disappeared. The same applies to "R". (I haven't tried other marks
   yet.) Why?