How to Prevent Customers using our Reply to Email to create new incidents ?

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We want our customers to use our webform exclusively. The webform has categorisation and workflows to the relevant functional area based on the enquiry type.

When anyone replies to a customer, of course you need to have a reply-to email for the customer to respond back to. We have a branded one directed to our custhelp mailbox.

The issue we are having which is getting bigger and bigger, is that customers are latching onto this email and using it to create new enquries.

Is there any way to prevent this ? Is there any way to configure things so that a mailbox only accepts replies and not new enquiries ?