Even if a message is enabled, it still needs somebody to deliver the message to. This is controlled through the Subscribe and Block features of the Message center. The actual email address that is used for the sending is obtained from the user information. There are four links for subscribing and blocking messages. These all perform the same basic function.

You can subscribe people to a message either by individual user ID, or by group ID. It may happen that an individual is subscribed to a particular message both by individual user ID, and because they are a member of a group that is subscribed. If that is the case, they will still only receive one copy of the message.

You can also block people who would normally receive a message from getting it. This is particularly useful if a person is a member of a group that gets a message, but really does not want to be bothered by that message.

A person can be added by the slot code when the message is queued. This is used for example, when a new person signs up, and we want to send them a welcome message.