You can do both on one machine using multiple postfix instances, one
for incoming mail and another for outgoing mail, each running on its
own IP. But since you already have multiple postfix instances on two
machines it seems silly to complicate a working setup for little
gain, unless you're trying to get rid of the second machine.
Thank You for Your answer, that is exactly what i did, for now.
My goal was to get rid of separate machine for signing, so i made
second postfix instance that will handle submission and signing, leaving
first instance to incoming mail and verification. Only downside is that
this setup needs two ip addresses.
