A blacklist gives you the opportunity to block incoming e-mails from specific addresses. It can be useful, in many cases, to avoid commercial newsletter, spam or uninvited e-mails.
To create your blacklist login to your cPanel control panel and, in the "E-mail" section, click "Spam filters". 
Here, make sure that "Process new e-mails and mark them as spam" is enabled. If not, switch the icon from left to right to enable them. 
Once you've made sure of this, you can manage your blacklist by clicking "Edit blacklist configuration"in the "Additional configurations" section.
Here are a few examples of several addresses you can type in the text boxes next to blacklist_from fields:
- name@mail.est
- *@isp.com
- *.example.org
Then click "Update Blacklist" to end the operation.
The second and third option specify all the incoming e-mails from a specific web domain (respectively @isp.com and @example.ord). In the syntax accepted by system, ? stands for any general character, * stands for arbitrary length strings otherwise it's impossible to use regular expressions (Regex).
