[SOLVED]Postfix trying to send locally, not using MX records

I have a Ubuntu 10.04 LTS server that I've recently set up.

postfix seems to be running fine (I use it for outgoing only, I using Google Apps in the domain's incoming mail).

If I send mail from that server however (like just using 'mail xyzzy@foo.com' from the command line), it doesn't deliver the mail to google's servers.

I get a line in /var/log/mail.info: 'unknown user: xyzzy'.

How can I tell postifx that for foo.com (my domain), I don't want it to try and deliver locally, I want to use the standard MX records?