In your browser, navigate to the 1&1 Exchange account login at http://exchange.1and1.co.uk/
At the bottom of the login screen will be a link for XAdmin. Click the link to be taken to the XAdmin login page.
Use your 1&1 Exchange e-mail address and the account's password in the respective fields. Click the Log On button to log into XAdmin.
You can now begin management of your Exchange account from XAdmin.