What is the Criteria or a cease and desist letter

There are no criteria for writing a letter.  You want someone to stop doing something, you, or your attorney, write them a letter asking them to stop.  Getting a court order to force them to stop is a much different proposition, particulalry when you are asking the Court to prevent someone from exercising free speech, and particularly when you may have other means to stop the communications (e.g.. can you change your phone number or email addres, or block them as a sender?).  To do so you would have to show that the person had done something wrong, not just in poor taste, i.e. was defaming your daughter (which requires a falsehood; the truth, however embarassing, is not defamatory), was disclosing information which is either required to be kept confidential by law (i.e. medical informaiton protected by hipaa) or by contract (e.g. an n.d.a). or some other wrongdoing (e.g. the person trespassed on your property to leave a note in your mailbox)..