First you have to find them. Many e-mail service providers' tools can give you access—for example, allowing you to identify those who haven't responded by campaign or to create a list segment called “nonresponders.”
Now the fun begins: Once they are segmented into their own categories, start testing things on them to get them activated. A few things to try:
1) Send an e-mail with a link to your opt-in form to reopt them in. On the page with your opt-in form, give examples of your hosted e-mails so that they can see the real value you're providing.
2) Send an e-mail and include a coupon for your product or service. Maybe go overboard to really draw their attention: Give them something for free or just a really great offer.
3) Maybe they have a new e-mail address and just don't check the one you have. If you have their telephone number, why not call to ask if they've got a new address and want to be readded to your list? If you've got their postal address, send a postcard directing them to a coupon or offer.
4) Send a survey to find out why they aren't responding. Try a direct subject line like “Why haven't you opened our e-mails? Tell us.” To pique interest. You might want to have an open-ended question box here since you won't be able to guess all the reasons in advance.
Purging these names out of your regular mailings will surely give you an increase in your open rates, but the real key is to try to move these nonresponders to “responder” status.
Janine Popick is CEO and the founder of e-mail marketing company VerticalReponse, www.verticalresponse.com.