You can use spam filter to block emails by size.

1. Login to your DirectAdmin account.

2. In the Email Manager section, click on the Spam Filters icon or type “Spam Filters” in the Navigation Filter box and the option will appear. Click on it.

   

3. Under “Block By” from the drop-down menu, choose the Size option.

4. Under “Value”, choose Size in KB or MB and enter your value.

   

5. Click on the Block button.

If you have chosen size in MB and have entered the value 5, for example, all emails exceeding 5 MB in size will be blocked.