How can I add another Exchange account to my existing package?
Log in to the 1&1 Control Panel using your Customer ID OR domain name and your password.
If you have only one package, you will land on the Administration page. If you have more than one package, select the package in question to reach its Administration page.
Click Order More Features from the My Data section of the 1&1 Control Panel
Find and click the Microsoft Exchange Account button and then continue with the checkout process.