I have never heard of anyone getting an E-mail message giving an harrasment warning, the issuing officer should have had all your info and paid you a visit and served a form on you , doing it by e-mail does not to me seem right. These sorts of things should be done face to face in my humble opinion. e-mail copies between you and the complainant ? well have you not kept your e-mails and replies then ?
It may prove to be the process that force use for some reason ( Which force is it ?)
you need to speak to the officer in person, dont simply reply to an e-mail.
I am not a regular patrol officer ( I am on traffic so dont deal with these things from day to day) hense why i did not reply earlier