The Bogofilter plugin provides anti-spam capabilities for Claws Mail. Bogofilter is a pure Bayesian filter, written in C, which makes it very fast. Claws Mail also provides a SpamAssassin anti-spam plugin, with the same feature set, but more extensive 'spaminess' checks. The Bogofilter plugin features are:

• Filtering spam when mail is received, moving it to a specific folder, or destroying it completely,
• Learning what is spam and what is ham, in order to better filter your mailbox.

Before Bogofilter is able to function effectively, you have to show it a few of your spam emails and a few real emails. You can do that by selecting some messages, right-clicking on them and choosing 'Mark/Mark as spam' or 'Mark/Mark as ham'.

Bogofilter is required, https://www.bogofilter.org/

Here are a few screenshots illustrating the features:

• Initial learning: Showing Bogofilter some real emails.
  
   
   
• Helping Bogofilter learn from a missed spam.
  
   
   
• Checking for false positives in the Spam folder. Looks like Bogofilter did a good job…