An incoming message and an indication of a sender-specified destination for the incoming message are received. In addition, a determination is made as to whether a mobile telephone number is known by the sender to be associated with the sender-specified destination. If a mobile telephone number is known by the sender to be associated with the sender-specified destination, a first message that is based on the incoming message is sent to the mobile telephone number. Furthermore, a second message is sent to the mobile telephone number that indicates that the first message was sent to the mobile telephone number based on a determination that the mobile telephone number is known by the sender to be associated with the sender-specified destination.