How to Transfer Xbox Account to New Email?

How to Change Your Email Address on an Xbox One

While still logged into your account, click "Your info" and then select "Manage how you sign in to Microsoft."
Click on "Add email" and create a new Microsoft domain email address or add an existing Microsoft email address.

Can you Transfer an Xbox Account to a Different Microsoft Account?

Unfortunately that is not possible. Xbox accounts and Microsoft accounts are essentially the same thing. Nothing can be transferred between accounts.

Can you Change your Xbox Email Without Losing Everything?

EDIT: Yes, everything seamlessly transfers over to your new e-mail.

Need to Change the Xbox Gamertag to my Sons Email Address ...

Sign in to your account using your existing alias and password.
Go to Your info at the top of the page.
Select Manage how you sign in to Microsoft.
You may be asked to verify your account before changes can be made. Follow the instructions provided to select your alias: Select Add email.