You can customize attachment restrictions on your domain via the Attachment Restrictions option.
To begin customizing,
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Navigate to Attachment Restrictions from the dashboard under Incoming - Protection Settings.
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By default SpamExperts already have multiple extensions listed. -
To add extensions manually, Add the extension name under Add New Extensions.
Should you wish to remove the extensions from the block list, checklist the extensions and click Remove Selected.

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Finally, click Save at the bottom of the page.

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To disallow sender from your domain to release messages that contain attachments with certain extensions, go to the Disallowed Release Extensions.

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Under Restriction Options
You can block mail that has :
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Password protected files.
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Potentially unwanted attachments such as compressed executable files.
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Hidden executables.
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Attachments with macros.
Don't forget to click Save at the bottom of the page after done checklisting. -