TAD mode is the only mode that can be used with an external telephone answering device (unless you are using a distinctive ring number for receiving faxes). Your telephone answering device must be connected to the jack on the Brother machine (labeled "EXT" for USA). When someone dials your telephone/fax number (to send a fax or to speak to you), all the telephones (including the FAX) will ring according to the number of rings you set on the TAD. The Ring Delay setting is not recognized in the TAD mode. If you do not answer the call, the TAD will answer. As your outgoing message is playing, the Fax is in the background, silently listening for fax tones. If the FAX hears fax tones, it will automatically go into the receive mode. If the FAX does not hear fax tones, it remains silent, allowing the caller to leave a message.