To turn on/off a rule, follow next steps:

This rule is useful if you receive a lot of messages from your colleagues and use rules to copy or move correspondence to the specific folders (like Rule to copy all correspondence on some subject to the specific folder or Rule to move all correspondence on some subject to the specific folder). Unfortunately those rules do not work for messages with an empty subject, but you still can create a rule to send an automatic response if the incoming message does not have a subject.