Log in to 1and1 administrative console at http://www.1and1.com/login by entering your 'Customer ID' (Account Number or Domain name), 'Password' and clicking 'Login'
Click 'Administration' tab
Click 'Domains'. The 'Domain Overview' page will appear
Choose the domain for which the MX records are to be updated
Select 'Edit DNS Settings' from the DNS menu
Click 'Advanced DNS Settings' and choose 'Other mail server' from the options
Delete the existing MX records
Tip: If you do not want to delete the existing records at this moment, you can set them with lower priority. Edit the 'MX Records to set the priority with higher numbers like 10, 20 and so on for the existing records. You can delete these records at a later time after your changes have taken effect.
Enter the MX 1,2,3,4/Prio fields with the following information.
The MX records for your domain are updated now. But it may take up to 48 hours for the changes to take effect.