Yes, you have the option of having the system automatically lock outgoing users if they are misused for sending spam messages. Furthermore, you can set individual connection limits for individual outgoing users, which will also result in a lock if they are exceeded. Further information on the automatic lock can be found under "Settings for the outgoing user" in our FAQ article "How do I set up an outgoing user?".
Activating the outgoing connection limits only checks a user's connections to our system. The value does not determine how many messages can be sent by a user.