Whole functionality is handled by the extras-notify-acc-creation-processor processor. This processor sends notifications to users at the creation of their account on a particular system or systems, depending on the configuration.
There may be a need to not send this notification in some particular cases. In order to prevent the notification from being sent, you can set extras-notify-acc-creation-processor-skip=true property to the related event, which will make extras-notify-acc-creation-processor not notify the affected user.