Here are some good suggestions from Sundeep Kapur of www.emailyogi.com: When someone unsubscribes from your email list, don’t simply remove them. First, send them a confirmation, and include an offer. You may actually be surprised at the sales you get.
Second, keep a record of your unsubscribes on a master unsubscribe list. Make it manual process to remove anyone from the list.
Third, if the economics of what you’re selling warrant, use postal mail to try to re-engage your unsubscribes.