Our mail server currently has a entry for NAT ( binded to
the Pubilc interface and (Exchange) to the private. There
are filter sets that pass traffic port 25 from public to Exchange.

We have a new spam filter applicance ( that needs to sit
between Exchange and the internet. I have added a NAT entry for this (Public) to (PRIVATE).

Do I need to simply adjust my filters to specify the new appliance which
will be a mail relay or do I need to adjust the NAT table and bind to (new mail host)?