There has been an initiative here at my company to drum up sales through contacting users who have purchased form us on our website(s). The subscriber (purchaser) listing I have dates back to 2002.
My question to you all is this:
At what point does it become unethical to contact your purchasers from the past? 2 years? 3-5 years? Ever?
Good question Mike. Practically, the longer you leave it the less likely people are to be happy about it. Obviously the product itself is relevant too - someone who bought a house from you a few years ago might be happier to hear from you than someone who bought a toaster.
I'd love to hear from other people too.
Mike, our permission policy stipulates that you can never contact anyone who gave you their permission more than 2 years ago and you haven't contacted since. Permission really doesn't age well, and to avoid complaints I'd even consider shortening that time frame even more.
To build upon Mat's points, it really all comes down to common sense. Put yourself in your customer's shoes (as in, pretty much forget that you exist) and then make the call on what is and isn't reasonable. Hope that helps.