Allowing recipients to forward a newsletter or any other type of message you send them gives you the chance to expand your readership and donor base. Take the time to consider why you are interested in tracking recipient interaction. Is it your primary goal to develop statistics on user behavior, or are you trying to figure out what your base is interested in so you can more easily expand your readership and donor base?

Lastly, adding the ability to forward an item presents almost zero cost on the programming end and on the user interaction end. It merely gives the user more opportunity to spread the message you are trying to get out.