[Mimedefang] OT: [sendmail question]

[Mary Verge DeSisto]

Setup: external mail servers(sendmail 8.12.10) relay email, via mailertable, to 
internal mail servers.  Internal mail servers run Mimedefang and send mail to 
exchange server.

Problem I am having is that we have a product that allows our customers to email 
content to themselves.  It produces tons of returned email because of various 
customer sites not accepting email with service unavailable, etc. I want to drop 
these returned emails at the external mail server so that my Mimedefang server 
does not have to process them.  I tried adding the email address the returned 
email is coming to to aliases(/dev/null) and my access db(DISCARD).  It seems 
that both are not accessed when sending/relaying mail via mailertable.  Anyone 
know how I can drop this email at the external server?

Any help is appreciated.
thanks and sorry for the OT,
-Mary