After using SpamSieve for many many years with Mail.app, I moved to Airmail a few months back. It’s not clear to me whether SpamSieve starts over with a new email app; but I’ve been trying to correct false positives to no effect. It seems that this doesn’t work as well as it did in Mail.app. Any advice?
The SpamSieve training data is automatically shared between Apple Mail and Airmail. You can use the Open Log command to see whether SpamSieve had predicated that message to be spam and whether Airmail successfully told it to train as good.