Hi,
... not sure if I completely understood you.
You can specify headers if you're using the mail function. In this case you can specify a custom From: header.
There are some examples here.
But mail servers might refuse to accept a mail for delivery if the domain part of the sender email can't be resolved. So in this case you might need to set the From: header to another email address because unix-22.vhostnix.com doesn't seem to be externally resolvable.
Thomas