You can block and approve Domain/IP's or Email Addresses within the Control Panel.
Log into the Control Panel and click More Services.
You will find some details regarding your account here.
To always accept emails from a domain click Approved Senders
Click Add New Entry
Either enter either the domain, email address or IP address of the sender, and a short description then click Submit.
To always block messages from a domain click Blocked Senders
Click Add new Entry
Enter the domain, email address or IP Address you wish to block, and a short description. Then click submit.
Once you have added either the approved or blocked sender they will appear like below, under the relevant tab.