For setting an alias in Google Mail, follow these simple steps:
1. Sign in to your Goggle Admin console
2. Go to the user’s account page
3. Click Account
4. Look for Aliases section and click “Add an alias”
5. Enter the desired username in the text box that will appear.
6. In case of multiple domains, choose the desired one from a list of domains available.
7. Click “Save Changes” andthe change will take effect.