pop3-leave-mail-on-server but mark it as read ?

[lgfang]

I'm using gnus reading pop3 emails.  I add following line in my
.gnus.el so that gnus won't delete emails from pop3 sever.

,------------
. (setq pop3-leave-mail-on-server t)
`-----------

The problem is that every time I run gnus-group-get-new-news, all
emails which had already been read will show up again.

So I'm wondering if there is any way to mark the emails (at pop3
server) as read so that next time I run gnus those which had already
been read won't be downloaded again.

Regards,

-- 
When all the tool that you have is a hammer, every problem looks like a nail