Function folder 

pub fn folder(
    account: &Account,
    folder: &Folder,
    cards: Vec<Card>,
    trusted_ids: &[String],
    words: &Words,
    all: bool,
    query: &str,
    tr: &Translator,
    now: i64,
    sent: Option<Vec<Card>>,
) -> FolderView

What a folder shows: all past the last two weeks; query searches every message kept, by sender, recipient and subject. With sent (the account’s Sent folder), messages are shown by conversation, your answers among them.