Filtering Tickets based on Email headers

We're starting to get a lot more junk coming into our Zoho Desk, which is then triggering unnecessary email alerts to agents. Once thing we could do to cut this junk in half, is to filter tickets based on email headers.

Any email containing the `List-Unsubscribe` header, is a marketing email, not a support one, and can be junk'd.

Any email containing one of the several `X-Auroreply` headers, is just an out of office or similar, and can be ignored or junk'd depending on if it's a new ticket or a reply to an existing one.

I cannot see any way to do this using the Workflow rules. So i'm wondering if a custom function would do it?

I can't seem to find any specific docs on custom functions, what they can and can't do, what functions are available, what the input parameters are, can they retrieve an email header list, do they return a boolean decision to the workflow pipeline, or do they apply the action to be taken themselves?

Any guidance on (a) if this is possible with a custom function, and (b) a steer on how to achieve it, would be gratefully received.