How does spam filtering work? It doesn't seem to learn at all

[lifeboy]

I use pmiab with Thunderbird and have a spam folder designated for spam. When I go to my spam folder and maark something as not spam, within seconds it gets marked as spam again. I can repeat the process many times, and the result doesn't change.

From what I understood, spamassassin "knows" that I mark mails as not spam, so why doesn't this work as I expect it to work?

[lifeboy]

I may have found the cause. Thunderbird has an option to honour spamassassin's assessments which is turned off my default. I enabled that and it seems to make a different. I'll monitor it for a few days and see if that solved the problem.