maybl8 Do I need to clean this up from time to time.
Yes. There is no auto-deletion, except you configured a cronjob accordingly.
If I do clean it up will it stop moving similar emails to junk?
Bayes won’t be learned in any way if you delete emails from junk - they are just being deleted. Only when you move emails from somewhere to Junk, they will be learned as Spam. As ham when you move it out the Junk folder.
Some similar spam emails get into my inbox and I move them to the junk folder. How long does it take to recognize these similar emails and spam and auto move them to junk?
Bayes kept the training data for 30 days. It was bumped to 90 days in 2024-08a, if I recall.
What are the best server settings for stopping spam emails?
Defaults usually good balance. But you can change your own score to mark as spam when editing the mailbox.