[Mimedefang] Question about bounces - How do I do this?

[Troy Carpenter]

I have tried different approaches to this problem, but I haven't yet
figured out how to do this (mainly because the situation does not happen
all that often, but I still want to handle it).

My mail server is only used by my family.  However, since some of my
family members (parents, uncle, brother) do not live with me, they use
their own ISPs for email.  My system simply forwards email to their ISP
mailbox.  I am doing this via the virtualuser table to avoid creating
local accounts on my Linux box.  For instance, "dad at carpenter.cx" would
be forwarded to "dad at hisisp.net".

The end user, "dad" in this case, would put "dad at carpenter.cx" as his
return email address in his MTA. He still uses his ISP's SMTP/POP3
server for outgoing/incoming messages. 

This works great and all email bound for "dad at carpenter.cx" gets
delivered correctly except in one case...bounces (both permanent and
temporary).

Now, I can relay email through my ISP's mail server all day long, as
long as there is a from address.  However, my ISP will not accept
messages from "<>" if the destination address is NOT local to my ISP,
even if the relay address is in the ISP's address space (as mine is).  I
don't think that violates the RFC requirements about accepting bounces
since the server DOES accept the bounce messages, it simply does not
accept bounces not destined for a user in its email space.  (Come to
think of it, bounces generate by my system not as part of the SMTP
transaction would also fail in this scenario...like 4 hour warnings and
such).

What I am looking for is a way for MIMEDefang to intercept the "<>" in
the from address and change it to my system's email address (or better
yet, the postmaster address of the system which originally bounce the
email if possible) so that my "external" family members will know when
their email bounce.  I don't care if their MTA's don't recognize the
bounce and but fancy icons or whatever...getting notification like this
seems better than having it get stuck in my system because the relay
won't accept it.

Thanks for any info in advance,

Troy Carpenter
troy at carpenter.cx