[TriLUG] postfix - eliminating or munging return-path header

[Thunder Bear]

Hey has anyone here had an issue where the return-path was being
inserted by Postfix incorrectly, using a private domain name instead of
public domain?  I'm having some difficulty finding doc online of anyone
else having this problem.

Say, for example, my public domain is yonderway.com and my intranet
domain is yonderway.priv.  Outbound messages are being munged by Postfix
to have "Return-path: <thunderbear at mailhost.yonderway.priv>" which
causes some remote hosts to reject mail from me since they cannot
resolve mailhost.yonderway.priv.  I cannot for the life of me find
anything in the postfix config files that would set that line up, and
the best I can figure is it is doing a reverse lookup of its own private
IP address to get that hostname.

I'd like to either eliminate that path or fix it to use the public
domain name.