Hi,
I think I saw such thing in Zimbra and that Google have something similar; some sort of search-criteria based folders. That is to say, messages that matches a set of criteria are viewable under a special folder. This feature could be very interesting when you're subscribed to mailing lists. Do you think it could be easily done using informations from the cache ? I do not have significant PHP experience so I don't think I'm gonna try to add this feature.
Thanks
PS: in the hope you'd understand my poor english.