qmail and multiple interfaces

[Claudiu Balciza]

Given some multiple interfaced machine, I would like to know how can I
restrict the qmail to send messages only on one of them.
The real situation is that one interface has real ip address while the
others can reach out through masquerade.
Some mail servers use to check up the existence of the source host. This
fails on masqueraded addreses.
Any hints ?

Claudiu