Try this: http://sourceforge.net/projects/imap-agent/


>From: Jon (usenet@netacclaim.co.uk)
>Subject: IMAP proxy?
>Newsgroups: comp.mail.imap
>Date: 2004-02-24 04:55:02 PST
>
>
>Hi,
>
>I'm looking for an IMAP proxy to sit between a client and a server and
>provide mail-filtering capabilities en-route. Anybody able to point me
>in the right direction? :-)
>
>Cheers,
>
>Jon