Alliance email

How do I set the alliance email associated with the account to be the main email.
Ex: 123@gmail.com is the default but I’d like 123@xyz.com be the the default when creating an email within the 123@gmail.com account. 

Hi Scott, do you mean alias?
You can setup your aliases for the account under Tools > Account > Your account > Aliases.

Just add the aliases you have associated with your account, and when you compose a new message, all the aliases should be listed in the dropdown for “from:”.

Hope this helps,
Paul.