Gmail, Add Additional Email Alias

Gmail Admin

https://admin.google.com

Add an email alias for a G Suite user

You can add up to 30 aliases for each user.

1. Sign in to your Google Admin console.
2. From the Admin console Home page, go to Users.
3. In the Users list, find the user. If you need help, see Find a user account.
4. Click the user’s name to open their account page.
5. Click User information  Email aliases. 
6. Click Alias and enter an alternate user name (the part of the address that appears before the @ sign).Note: You can’t create an alias currently assigned to someone else, either as a primary address or alias.
7. Click Save.

Within 24 hours (and often sooner), the user will begin to receive email sent to this address.

Note:

Make sure to hit the “Save” button after you have enter in the new email alias.

Sources:

https://support.google.com/a/answer/33327?hl=en