Google Apps update alerts: Multi-domain management now available in Google Apps: "To add another domain:
1. In the Google Apps Control Panel, click ‘Domain settings’, then ‘Domain names’.
2. Click ‘Add a domain or a domain alias’.
3. Enter the domain name that you want to add in the text box.
4. If you just want to add the domain as a domain alias, enable the checkbox ‘Make this domain an alias of my primary domain’.
5. Click ‘Continue and verify domain ownership’ to verify ownership of the domain
6. Follow the instructions to verify domain ownership and set up email delivery."
