The Python project that's clent side? Best of my knowledge it hasn't been updated in years, spamassasin's in built Bayesian classifier works just fine.
I still used spambayes up until I basically abandoned my self-hosted e-mail setup (in favor of an @gmail).
It occurred to me recently that LLM-style tokenization + bayesian classification would be a sweet upgrade for spambayes, which always struggled with ad-hoc tokenization rules.
(I don't think of it as "client side"; it was integrated with my system via procmail on what I'd call the "server side". You could use it in other ways, including as an Outlook plugin, way back in the day. Or it could connect to an IMAP mailbox and filter messages it found, etc. Really versatile tool for its time)