Managing all your domains
Does your organization own multiple domain names where you do business? Perhaps you acquired a new company or started doing business under a new name. Google, for example, owns the domains google.com, adwords.com, youtube.com, and more. If you own multiple domains, you can add them all to your Google account at no extra cost. Users can then have an identity at one or more of your domains. They can share Google services as part of one organization. And you can manage all your users and domains domains from the same Admin console.
Add a domain as either a domain alias or separate domain as follows:
Let's say your business acquires a domain for a new brand, and your users need the option of sending mail with an email address at that domain. Add the new domain to your primary domain as a domain alias. This gives all users in your primary domain an alternate email address at the alias domain.
Let's say you acquire a new domain for a business that has its own set of employees. To let the new employees use Google services along with the users in your primary domain, add your acquired domain as a separate domain. Users in each domain will have an email address and Google account at their respective domain. But they can find each other in global contacts, meet via Hangouts, and otherwise collaborate internally using your Google services.
To use Google services with a new domain name instead of the one you signed up with, we recommend you simply add the new domain as a domain alias. Users can then begin sending mail using an address at the new domain. If you want to use custom web addresses at the domain, however, you'll instead need to sign up the domain for a brand new Google account. Follow the link above for details.
You can add up to 600 domains, including 20 domain aliases, to your organization's Google account. You must own the domain name whether it's used as a separate domain or a domain alias. In either case, Google will ask you to verify domain ownership.