I'm trying to find a way to eliminate duplicate email messages.

I can do this easily in procmail with the following rule, but am unable to have users call procmail from Zimbra, and can't find a "No Duplicates" feature in the mail filters section.
:0 Wh: msgid.lock
| formail -D 32768 procmail.NO_DUPLICATES_MESSAGE_ID_CACHE

Is there any way to do this today?