Start by checking Mercury logs to see where the problem occurs. Try to follow the message from when it's received by MercuryS to when it's accepted by the relay server, and note any errors that appear. Post log excerpts here if you want us to help you figure it out.

/Rolf 

I'm using Mercury/32 4.72 on Windows 2008 Enterprise.  I'm only using MercuryS and MercuryC as all I want is an SMTP relay.  I have *no* users outside of the required Admin and there are only two email addresses that matter.

 I set up an outgoing filter to forward all messages with "one@company.com" in the "To" header (exact match) to "two@company.com"

 "company.com" is NOT the domain that Mercury is servicing.

 When I send an email to one@company.com, it is endlessly forwarded to two@company.com - thousands upon thousands of times.  Obviously I only want it forwarded once.

 Any clue what I'm doing wrong?