What does the "stop" command in dovecot sieve do?

Question

There's a command in the rules file called stop, which stops processing. I'm not sure why this is needed though. If it's the last command in a list of directives within a rule, then isn't the rule already done processing? Or does it mean don't skip to the next rule in the list? In other words, let's say my sieve file has a list of rules:

Rule A
Rule B
Rule C
Rule D

If Rule B has a stop command at the end, will rules C and D be skipped? And I'm assuming rules are executed in the order they appear in the sieve file?

Answer 1

Yes, if rule B contains the stop command at the end, rules C and D will be skipped.

The "stop" action ends all processing. If the implicit keep has not been cancelled, then it is taken.
— RFC 5228 section 3.3 "Control stop"

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This is useful when detecting spam and a using a vacation message or some fileinto rules. You can discard the spam followed by stop which skips all following rules meaning you are not going to reply to them via your vacation rule and they will not be put in another mailbox via fileinto rules.

If you are using if and elsif you can avoid this problem.