nnimap two-level expiry?

[David Abrahams]

I don't know if this is possible with nnimap, but I'm hoping someone can
tell me how to do it.  IMAP allows you to mark messages deleted and
then, sometime later, actually flush or "compress" the folder to remove
them completely.  I'd like expiry to do something like:

* mark all read articles as deleted
* actually remove all deleted articles over one week old

Is that, or anything like it, possible?

I realize that Gnus can hide read articles (very nicely!) but I need to
use other mail clients too (e.g. iPhone, RoundCube webmail), and they
don't always give me a good way to avoid looking at things.

Thanks in advance,

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com