Function train_with 

pub fn train_with(
    dirs: &Dirs,
    trusted: &BTreeMap<String, Vec<String>>,
    options: &Options,
    errors: usize,
    progress: &mut dyn FnMut(&Progress),
    cancel: &Cancel,
) -> Result<(Summary, Detail), LearnError>

train, and what its test said message by message (detail): the test messages counted by account and folder, the grid of thresholds, and up to errors errors of each kind, your own mail’s and each outside source’s, as the model learned from the oldest 80 % judged them.