Login to your account at Heart Internet.
Under Manage Domain, click DNS Management.
Under MX Records you need to delete the current MX records and add our MX servers according this list:
|MX records are specific to individual domains, please login to view the MX servers for your domain.|
Continue adding the three MX servers in the above list, when completed you will end up with a list of MX records that look like this sample:
Your MX records are now configured, your email will be protected by MX Guarddog. Changes may take 24 - 48 hours before all computers on the Internet see the update so some spam may continue to reach your mailbox during this period.