Exchange 2003 email bouncing from a public folder

I am having a rather annoying problem within Exchange 2003. At the moment, mail comes in on [email protected] which is picked up by a public folder which everybody has access to. This is auto forwarded (in delivery options) to [email protected]. This works perfectly fine, however, somehow an email will additionally get sent to other email addresses, these are people that have left the organisation, and therefore have no user account, nor email addresses. The email then bounces back to [email protected] which is auto forwarded to [email protected].

This has become very annoying, and I cannot find where this is occuring in exchange. My last thought is that somebody has setup an outlook rule (client/server side) which auto forwards these emails to these non-existent users. If this is the case, is it possible to find out which user has done this?

Many thanks

Alistair