It's no big news that email lists can go cold. It can happen for any number of reasons. Maybe the list building process took longer than you expected, maybe your boss wasn't ready to pull the trigger on email marketing when the list was forming, or maybe you've just bored your list to tears. Regardless of the reason, you can heat your list back up with some fairly easy methods.
Communication is key. While you may think that asking your customers directly will make you look bad, it doesn't. They will respect your honesty and if they do have an issue they will know that you care and are making efforts to correct it.
Even if a customer has begun to ignore your email, a particularly good incentive can bring back even customers with the most waning interest. If someone was at one time interested in what you have to offer it's very likely that they will be again under the right circumstances. Give them a reason to come back.
If providing one kind of promotion doesn't seem to be exciting your audience, try something new. Maybe your recipients are still interested in buying something from you but have just grown tired of the same old offers. If you send them a coupon for 10% off every time, it's not going to be much of an attention grabber after a while. Consider changing up your offers and occasionally doing something very unique to make your customers do a double-take when they receive your email.
While content may still be king, good looks certainly can't hurt. If you aren't seeing the results you want from your campaign, you may consider taking another look at your email design. A really bad design, and trust me they are all over the place, can scare someone away faster than just about anything. If you want your consumers to trust and respect your company your email should have a design that promotes you in the best light, not as some two-bit spammer.
Their wants, needs, and how they interact with your company/organization may have changed over time. What was once a popular subject among the people on your list may now be sorely out of date. Make sure you stay current with the interests and trends among your list. Keep your products and ideas up to date. If possible you could offer incentives to some of your recipients for filling out a survey. A great way for retailers to get people into their store is by giving out a five dollar gift card. Since barely anything costs just five dollars, it's pretty likely they will be spending some of their own cash once they get started.