Configure Google email delivery

To have email delivered to your users’ Gmail inboxes, you need to update your
domain to route email messages through the Google Apps mail servers. To do that,
you use the administration console for your domain to create mail exchange (MX)
records that point to the Google Apps mail servers.

• Ready to start delivering email to Gmail accounts? Creating MX records gives step-by-step
  instructions for creating MX records.
• Know how to create MX records? Google Apps
  mail servers provides the necessary details about the servers.
• Need more background? Understanding MX
  records explains how MX records work.

Don’t want to deliver email directly to users’ Gmail accounts? Email delivery options describes more
advanced forms of delivery.

Visit:- http://www.google.com/support/a/bin/answer.py?answer=33352