For several versions of Mail, you’ve been able to select a message and in the Menu Bar you would choose Message > Move To Predicted Mailbox to file the email in the suggested mailbox. If the Move To command is disabled, this means the Mail app hasn’t yet learned how to move messages like the selected one. Once it sees you move messages from your mother into your Family mailbox, for instance, it will suggest that destination in the future. In Mojave’s Mail, there’s also now a Move To toolbar button. If it can predict where the message will go, just click it; if not, click and hold to bring up a menu of all your mailboxes.