Go to the respective URL as per your MX record:
For MX1 & MX2
For MX9 & MX10
For MX11 & MX12
For MX14 & MX15
Username: Email Address
Once you are logged in Click on the Manage White/Black List Option
If you wish to White list any email address/Domain Name, Just add the desired information in White list Tab and click on save.
Similarly, If you wish to Black list any email address/Domain Name, Just add the desired information in Black list Tab and click on save.
While white listing /Black listing any email address (Example: firstname.lastname@example.org) Type the complete email address and click on Save.
While white listing /Black listing any Domain name, Type Domain Name starting with ‘@’ sign (Example: @domain.com) and click on Save.
Note: If Domain is added without “@” it will save but will not be functional.