Sending mail through certain IP

I have a linux (debian 3.1) machine with 2 IPs (first we call 1.1.1.1 with host: host1.tld the second we call 2.2.2.2 with host2.tld).
the project im talking about is "on" my second IP. I set up an apache (2.2) virtualhost only listening on this IP (2.2.2.2). If I use this drupal-module sending an email thru googlemail-smtp it works BUT: receiving the mail comes up with this headerinfo:
"Received: from host2.tld ( [1.1.1.1]) by mx.google.com with ESMTPS..." As you can see, the host is correct but not the ip :/

I only want to use this external-smtp method. And I want, that its used the correct IP for that job. So may someone help me out?

Thanks, so far