Mail rules in the Mail app on your Mac are robust and powerful but they no longer work well in a world where we get email on multiple devices. Instead, use iCloud email rules, or filters you can set on your email server. These rules will be applied on the server before the messages get to your devices, so they will work properly and consistently.
MacDailyNews Take: Thanks to Gary for yet another useful tip! We’ve got some old Mail rules to convert to iCloud email ASAP.