[Mimedefang] Allowing Users to get Quarantined Email from Relay Server

[Al Sparks]

Running spamassassin and MimeDefang on a linux box running sendmail. 
Sendmail is configured as a relay, that sends email on to a variety of
different small to medium sized Exchange servers, which are customers.

So far, we've been bouncing email with a fairly high spam score, and
letting the various Exchange spam filters take care of the rest.

However, the desktop folks now want to quarantine the spam instead of
bouncing it, and have a mechanism that a user/customer can grab that
quarantined spam.

Of course, it has to be user friendly (web based?) and preferably no
local access to the mail relay by customers.

Is there anything like that out there?  Will it work with SA / MD?
  === Al