If your email service supports Sieve scripts (for example, Fastmail or Proton Mail), you can use this filter [1] that I made. It's very aggressive and will block all emails that originate from Zendesk, so you'll need to disable it whenever you're actually expecting mail from Zendesk.
[1]: https://gist.github.com/hampuskraft/780c8fbcc4042689153533ef...
For those on Fastmail, here's a link to get to that setting directly: https://app.fastmail.com/settings/filters/sieve
Who knows when they’re emailing a mailbox behind Zendesk?