Often LTAs will create a mass of sock accounts to send abusive emails using the EmailUser function - having an option (similar to the new "Prohibit these users from emailing me:") to disallow non-confirmed editors from emailing you would be useful for regular targets of this harassment.
This ideally would be a global preference, but I appreciate that the definition of "confirmed" is not the same on every project.
Perhaps a local preference per wiki using the enwp definition (4 days + 10 edits) would be a good start?