An alias is just another name attached to your domain to form an email address.
For example, John Smith's username is jsmith.mygigemail. His default alias (sent in the From section on his email) is jsmith@mygigemail.com. He also has the aliases of johnsmith@mygigemail.com and john@mygigemail.com. John has a total of 3 aliases.
To add an alias to a user, go to Enterprise select the user you wish to modify.
1.) Go to Email Aliases and New Alias.
2.) Select the domain and format for the new alias, or enter it into the text box. You may also set a catch-all alias so all emails into that domain are delivered to that user.
3.) You can also set the default alias for that user by checking the box.
4.) Click Create.
To add an alias to all users, go to Preferences and Email Domains and Aliases.
1.) Select the domain to alias, and click on Alias all users.
2.) Select Yes, and Set As Default to set that alias as the sender address for all users.
3.) To simply add the alias to all users, click Yes.