By default Outlook adds “stop processing more rules” to message filters. Eventually I run into the error:

The rule has a condition the server cannot process. The action ‘stop processing more rules’ will prevent all remaining server rules from being carried out. Are you sure this is what you want to do?

Well… That is what the condition is to do, right?

So, it turns out the message does not describe the problem very well. What it REALLY means is that the rule is a client-side rule and will stop processing server-side rules, but the server has no way to evaluate the client-side condition. So everything could get confused. So either stop using client-side rules or stop using “stop processing more rules”. The latter is a default, so it is applied to almost all the rules. The former is a small fraction, so easier to expunge.

Feel like I learned this when I was using Outlook at my old job and forgot it because I switched to Mozilla. So I am having to relearn it.