Luminate Online will not send the same message to a constituent record more than once and this allows you to configure emails with multiple target groups where there might be overlapping members. This is useful for things like welcome series messages where you would not want to send a welcome message to the same constituent record twice.

There are some situations where a constituent might receive the same message more than once. For more details, see Why would a constituent receive the same email more than once? (BB747869).