If you are getting spam emails from the same domain but with random email users, you can block that domain from your DirectAdmin control panel.
Login to your DirectAdmin account.
Email Managersection, click on the
Spam Filtersicon or type “Spam Filters” in the
Navigation Filterbox and the option will appear. Click on it.
Under Block By, from the
drop-downmenu, choose the
Under “Value”, type the domain name without http or www.
If you want to block more domains, just repeat this tutorial from steps 3 to 5.