marking all article in 'expired' group as read automatically

[Francis Moreau]

Hello,

I'm trying to customize my 'expired' group so that any mails dropped in
this group will be marked as read automatically (ie without the need to
press 'C' on this group).

Is this possible (I know it is :) ?

The goal to do this, is to make Gnus move my emails marked as expired in
the expired group immediately and then let those emails during a grace
period (1 month for example) and eventually make Gnus automatically
delete the expired mails after this period.

Thanks
-- 
Francis