What is this Outlook "Rules" warning actually telling me?

I have an Outlook Rule that looks like this:

The text version is:

Apply this rule after the message arrives
  with Cron in the subject or body
and with Cron Daemon in the message header
  permanently delete it
and stop processing more rules

Now, because I am permanently deleting messages that match this criteria the "stop processing more rules" option in the "Select action(s)" dialogue is always enabled. My understanding is that if a message meets this rule, because it's being permanently deleted, there's no point processing any more rules for that message. That's fine and I totally understand this.

However when I close the Rules and Alerts dialogue box Outlook pops up this warning message:

The text of the message box is:

The rule has a condition that 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?

The part of this warning I find puzzling is highlighted in bold and italics above:

The action 'stop processing more rules' will prevent all remaining server rules from being carried out.

What is this actually telling me? It is confirming that:

• I have a rule that will stop any further rules being applied to a particular message once processed (and move on to the next message)?

or

• I have a rule that will stop any further processing, and, as the message seems to indicate, all remaining server rules will, regardless of message, no longer be carried out?

Which is it?

Outlook rules daisy chain, in a cascade, so each email is processed against multiple rules. To answer your question, the "Stop Processing rules" step applies only to the current mail, which meets the required criteria.

Any subsequent rule that might match that email will not be evaluated. that’s primarily what the message is telling you. The order of rules is important, and its logical that no rule can do anything more with an email once its been deleted, so once the rule is matched, it must either be the last one in the list, or the rules after it have to be skipped.

All the rules still remain active though, and when a new email comes in, they will process it until either reaching the last rule, or hitting a stop.

Frank and Tom aren't right on this one, well, Frank's right, but not answering the question with respect to the actual warning.

As Frank explained, and you alluded to already knowing, stop processing more rules does mean that, should it match, it will not process further rules.
But that isn't [just] what's causing the warning, and certainly is not what the warning is about.

To correct what Tom said; but maybe Outlook does this server side, I don't think it means this at all. Yes, it does (if you're using Exchange or Office 365), like sieve.
This is really handy if you check your mail on your mobile app, or the outlook website, as they don't process rules at all.

Unfortunately though, unlike sieve, it isn't super capable, and a lot of conditions generate a once-off warning saying this rule has a condition that the server cannot process, meaning, this rule will only work whenever you open Outlook on your PC.

I assume that searching for Cron daemon in the message header is one such incapability.
Now that's normal and fine, you check your mail online, your other rules still fire, and that one will too once you use your PC.

But now this is where this warning kicks in. You've also asked it to stop processing more rules, remember? We know the server cannot run this rule: So how would the server know whether to run following rules?
It doesn't and wont.

Basically it's trying to warn you that none of the rules after this one will be ran at all on the server, even if they could.
This mightn't affect you, so you may ignore it, but is a pretty important message if you:

• have auto reply rules or similar that need to happen immediately in response to emails and don't have your PC with outlook running 24/7
• use mobile devices to do quick checks of your email, but receive a tonne of mail and rely on filtering into subfolders/deletion for these checks to actually be quick
• or use browsers as the mail client more often than not

The Outlook behaviour for this is a bit silly.

The stop processing more rules option is on by default and it is usually what you want. Once a rule matches, it usually deals with the message and doesn't need to do anything else.

So given that, why would it give you this confusing warning every single time you apply an update to the rules. They should get rid of the message.

The "The rule has a condition that the server cannot process" is the most confusing part. The rest is unnecessarily stating the obvious.

Why can't the server process the condition? I don't think it means this at all.

Does it mean that the server processes the rules? I would assume it is the client that processes them (like Thunderbird), but maybe Outlook does this server side somehow.

Anyhow the "server" can process the rule, it just means that a subsequent rules will not be used because this rule is set to stop if it matches and does something.