expiring mail in Gnus

[Matthias Hertel <mhertel@bigfoot.de>]

Hi,

I'd like to configure Gnus to make reading debian-users somewhat
newsgroup-like, ie. all messages that are read (as opposed to unread,
ticked, or dormant) should be deleted from my disk after three days. I
thought that setting the following group parameters for my debian-users
group would accomplish this:

((to-list . "debian-user@lists.debian.org")
 (total-expire . t)
 (expiry-wait . 3)
 (gcc-self . none))

But it doesn't. Articles that are much older than three days and read
(appear as `O' when I open the group) don't get deleted. C-c C-M-x
(`expire all expirable articles') in the group buffer doesn't help
either.

I use Pterodactyl Gnus with XEmacs (potato), but I had the same
problem with the built-in Gnus in GNU Emacs (slink). As I do only read 
mail with Gnus, I have nnfolder as my select-method. Here's my .gnus:

(setq nnmail-spool-file "/var/spool/mail/mat")
(setq gnus-select-method '(nnfolder ""))
(setq nnmail-split-methods
      '(("debian-user" "^Resent-From: debian-user@lists.debian.org")
        ("jdc" "^To: JDC.*@sun.com")
        ("info-dylan-digest" "^To: info-dylan-digest@harlequin.co.uk")
        ("oreilly" "^To: .*@oreilly.de")        
        ("other" "")))
(setq gnus-message-archive-group "sent")

Have I completely misunderstood what Gnus means by `expiring' or is
there just some global setting that's meant to keep users from
inadvertedly turning total-expire on?


A somewhat related problem: Normally read and dormant messages are
hidden from the summary buffer. How do I *temporarily* make them
visible? There is a group parameter called `display' that controls
this, but I don't want to edit the group parameters every time I find
myself wanting to reread an article I read two days ago. (But I'd like 
to keep the short format as the default.)


Thanks
Matthias