I am looking for a method to eliminate or quarantine contacts that are automatically added to the CRM contacts from spam emails. 

The issue happens because we have both CRM and Desk with a two way sync. All emails that come into the customer service email for desk are synced over to the CRM.

I'm wondering if anyone has a solution for removing these contacts?

Is there a blacklist feature in CRM that I haven't found?

One method might be a macro or automated workflow that looks for emails marked as spam and then sets a custom field to indicate that the contact sends spam.

Or is there a way to catch it and stop contacts that are spam from syncing in the first place?

Thanks

Peter