two Return-Paths in email header

Hello there. I am fairly new to qmail and mailservers in general. I have
been working with qmail for a few months now and I quite like it and find it
is easier to use then other servers.

But I have encountered a problem that I need some help solving. I have set
up a mailserver for my internal LAN. Everything was working fine until I
decided to interact with the outside. I setup the qmail-masq package
(installed the QMAILQUEUE patch and qmail-filter). After a little fiddling
I manage to get it to masquerade my internal address for my external one.
But there was one small catch. The internet headers on the email had 2
Return-Paths. One was to masqueraded email address (expected and wanted)
and the other was the internal address (unwanted and unexpected). This
posed a problem since other mailservers where rejecting my mail because
their reverse DNS lookup failed because my internal domain does not exist.

I am not sure what more information you need configuration wise but I would
be more then glad to provide it if required.

Thanks

-- Ben Horan