We frequently attend conferences/shows/clinics where we have visitors fill out an offline opt-in form for our e-mail newsletter. We also allow them to sign up in our retail store. Are we required to keep these signed offline copies for a certain amount of time? Should they be archived for proof that these people signed up to be on our list in case there's an issue? We do, however, provide an easy method for unsubscribing from the newsletter. Any advice or resources would be much appreciated. Thank you