What causes Apple Mail rule to get turned off?

SpamSieve
,
1

SpamSieve was active until it wasn’t. I looked in the FAQ, and sure enough:

  1. If you are using Apple Mail and SpamSieve does not seem to be filtering your mail, please check the Preferences ‣ Rules window in Mail and make sure that the SpamSieve rule is active (checked).

Yep, that was it. But why? Is there a list of things I could do that would have a secondary consequence of deactivating the rule?

2

No, Mail just seems to forget which rules are enabled sometimes, even if you aren’t doing anything.