1. Log in your smarter mail admin, then select the domain you want to create the filtering rule.
2. Go to Setting on left hand side panel and select Domain Settings.
3. Choose Filtering , then click on Content Filtering.
4. Click on New, scroll down to find the Attachments . Tick on Specific extension and proceed to Next.
5. Key in the extension that you want to filter and save it.
Note: Apply only for Dedicated / Cloud hosting server .