For a domain alias or email alias you owned.
- Sign in to your Gmail.
- Click the in the upper-right and select Settings along the top of any page, and select the Accounts tab.
- Under Send mail as, click Add another email address.
- In the Email address field, enter your name and alternate email address.
- Click Next Step >> and then click Send Verification. Gmail will send a verification message to your other email address to confirm that you own it.
- Locate the message from Gmail. Open it and and either click the link contained in the message or enter the confirmation code in the Accounts section of your Google Apps email settings.