The old joke is, you know you need a vacation when you dial "9" for an outside line from home. I reached that point recently, so I planned a vacation to Hawaii. After a week of hiking Maui's remote shores, visiting dormant mountaintop volcanoes and staring at ocean sunsets, I was rejuvenated and ready to return to work. There are parallels between the human need to be refreshed and email marketing. One of the most evident is the tendency over time for email lists to become tired and lose their productivity. This happens to most lists at some time. While it's easy to tell if you need a vacation (for example, you look forward to jury duty) the signs may be more subtle when it comes to knowing your list needs a refresh. Here are three easy ways to tell your email list may need to be rejuvenated: 1. The open rate is trending down. The email open rate indicates how many people are opening an email. This typically is calculated as a percent of the total number of emails sent. Many web-based email clients block images by default, which registers as an un-opened email, so the open rate isn't 100% accurate. However, when looking at open rates over a period of a few months, a dwindling open rate may mean that your list needs attention. 2. List attrition is up. Unsubscribes coming through your preference center or the From Address are common. Email lists are living things, and the total number of subscribers can increase or decrease over time. An increase in unsubscribes over time, though, can point to the need to refresh the list. 3. Dwindling engagement. Engaged subscribers open and view emails. They interact with your brand by forwarding emails. They click through to your website. If your email service provider (ESP) provides you with an engagement score for your emails, note if the scores have been trending down, since this is a sign that your list needs attention. If you don't get an engagement score, ask your ESP representative to help you determine if your subscribers are engaged with your mailings. There are several things you can do if you find that lists are in need of a refresh. You can attempt to re-engage members who appear to have lost interest by sending them special offers or other incentives that aren't offered to more engaged members. You also can ask subscribers who have been inactive to opt-in to receive emails again. When taking this step, it's best to include a link to a preference center where subscribers can opt to receive emails less frequently or where they can indicate the kind of emails they want to receive, such as industry news, product announcements, offers, etc. Finally, if those steps don't work, it may be time to part ways with unengaged subscribers by removing them from the list. While the list size will shrink, engagement will increase and the list will once again deliver expected results.