Omar, you can create a domain event to accomplish this. In SmarterMail 16/17, go to domain settings > events. Create a NEW event and give it a name/description. Set the Event Category as User, the Event Type as User Added. Leave the condition as the default. Add a new "Send an email" action. In the "To Address" field enter #username#@#domain# (make certain to include the # symbols around username and domain). You can use the same formatting within the body of the message, if desired.