When send and received email from the outside there are some that contain attachment leading viruses. With reference to this it takes some action to block the attachment order is not accepted by the user.
Following :
- Open Zimbra Admin
- Click Configure | Global Setting | Attachment
- Move to the left side extension.
By default there are several extension suggested by Zimbra for in the block. If the extension that you want to block is not available then it could add a section to the right.
Check This Video :
How To Block Ekstension Attachment on Zimbra Mail Server