I’ve been using SpamSieve for years and this is the first time I’m experiencing this issue. Latest version of SpamSieve and latest Big Sur OS. Mail will crash after using it for a while and when I restart it will sometimes take a while to boot up. I do get a SpamSieve pop-up explaining the problem and it also says SpamSieve will take me through the steps to adjust my OS settings so it will work but I don’t see how to get it to actually take me through those steps.
I did already try manually turning on the rules under Mail preferences but then the problem came back.