By default the SpamExperts service filters inbound mail based on a mixture of advanced algorithms and junk email reports from users. However, you can also manually blacklist email addresses and domains if you want.
This is done from the spam filtering area of your control panel. After logging in select Virus and Spam Filtering from the top menu.
Select Sender blacklist.
You can now enter the details you wish to blacklist. If you wish to blacklist a whole domain, enter it without the @ symbol. For example, if you wanted to blacklist any messages from Gmail users you'd enter gmail.com
You can also upload a CSV file if you have a large number of senders to enter.