In Trend Micro Email Security you can use Content Filtering to block these double extensions. The following steps below shows how to create a policy for this.

1. Go to Inbound Protection > Content Filtering, and then click Add to create a new policy.

   

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2. Under Basic Information, complete the needed information such as policy name.

   

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3. Under Recipients and Senders, you may specify the user email address or domain for the targeted recipients, senders as well exceptions of the policy.

   

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4. Click on Scanning Criteria, select Advanced. Tick Attachment is, and then click on name or extension. A new window will open, where you can specify the criteria for the attachment name.

   

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5. Add the regular expression. Do the following:
   1. Tick Attachments named, place the regular expression below and click Add.
   2. On the empty field add the following regular expression "example\.(...)\.(...)".
   3. Click the Add button.

      You will be able to see the expression added on the list below.

      

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   All attachments with the following filename format <filename>.<3 characters>.<3 characters> will be triggered. For instance, the policy will be triggered if an attachment with "example.pdf.exe" as its file name is received.

    
6. Once done, click on the Actions tab. Specify the action for the policy when triggered. In this case, we will set it to Quarantine.

   

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7. Click Submit to save changes.