In George Romero’s original Living Dead trilogy, flesh hungry zombies destroyed civilization and were a metaphor for mindless consumerism. They could only be stopped by shooting them in the brain, burning it to nothing, or chopping it into smaller pieces. Inactive subscribers, let’s call them zombie addresses, on your email marketing file are very similar, but a lot less gory to remove. Back in September, I spoke at the OMMA show in NYC about how the ISPs are now using engagement metrics to filter and block email at a subscriber and global level (you can see the presentation here), and one thing they are paying attention to is how many inactive addresses you’re mailing. They do this to gauge the quality of your lists and hygiene practices, as well as to accurately calculate complaint rates. If that isn’t scary enough, inactive addresses also have a high risk of turning into spam traps which can negatively affect your deliverability. You should really focus on removing these zombie addresses that are alive on your file but not responding and eating away at the ROI of your email program. Here’s your 3-step action plan to survive the upcoming email zombie deliverability apocalypse.

1. “Organize before they rise!” Max Brooks, Zombie Survival Guide

There are plenty of items you should be doing to prevent your subscribers from turning into zombies. First off, get to know your subscribers. A study by e-dialog (“Manifesto for Email Marketers: Consumer Demand Relevance” June 7, 2010) showed that subscribers were more likely to open emails and remain active customers if emails showed what kinds of products they liked, appealing offers and whether or not they are a new or returning customer. The same study also showed the number one reason for subscribers to not open emails is because they come too frequently and because they were not interested in the product or service being advertised. Sending targeted emails based on previous email activity, preferences, and purchase history are essential to keep your subscribers active and not turning into zombies. Additionally, marketers should be optimizing frequency to prevent subscriber fatigue, or risk them being infected.

2. How to spot your zombies

Identifying a zombie is easy. If they’re dead and walking, eating people, or rotting and missing body parts while trying to approach you, chances are you’ll want to run the other way. Spotting a zombie email address on your file can be slightly more difficult. You should try to identify them based on business rules such as mailing frequency and offer type. We can bucket inactive subscribers into three primary camps:
– Haven’t opened
– Haven’t clicked
– Haven’t opened, clicked nor converted
Next you’ll want to define the thresholds and time limits for these buckets until you attempt to cure them of being a zombie, or if it’s better just to get rid of them entirely. You’ll want to touch your subscribers at least once a quarter, hopefully with content that is targeted based on the information you know about them (see #1). The largest risk category is that which have never opened, clicked or converted. You can be more aggressive in removing these from your file. If they’ve ever opened, clicked or converted, but have become dormant, you have to act fast before the infection takes over the subscriber and they turn into a zombie. Let’s take a look at some tools to help you out with that.

3. Must-have tools to survive the Deliverability Apocalypse

The first tool you’ll want in your arsenal is bounce processing with rules in place to not retry certain bounces after a certain threshold and time period has been met. The most important bounce to not re-try is the “unknown user”. These addresses no longer exist and email providers and ISPs calculate the percentage of your file that are unknown users and will start to filter or block you if unknown users comprise over 10% of your file. Worse yet, some webmail providers actually recycle these abandoned email addresses into spam traps. Once the address has been converted into a spam trap, they’ll never open or respond to your emails, and having just one spam trap on your file can cause you to get filtered, blocked, or blacklisted. Once you have a spam trap on file, it’s almost impossible to remove without some difficult work.

The second tool in your arsenal is the feedback loop. When a subscriber marks your email as spam in the webmail interface, ISPs will return that person’s address back to you to remove from your database. If you do nothing, they’ll likely start to ignore your emails, or complain further which reduces your deliverability. If you don’t know what a feedback loop is or how to sign-up for one, we put together this guide to help you out.

Thirdly, offer a preference center where subscribers can change their subscription choices such as message type, frequency, volume, or their email address. By giving your subscribers more control over how you interact with them, they are much less likely to report your email as spam to the ISPs, unsubscribe, and more importantly, they are less likely to become inactive.

Two of the most important tools you can use to remove these inactive accounts are win-back and re-activation campaigns. A win-back campaign attempts to entice those subscribers still “alive” on your file to perform some sort of action so you can correctly identify them from the zombie addresses. Some popular tactics include sending out a unique offer to them based on previous purchases, sending out a survey to find out what they truly want, or by sending content that is tailored based on previous activity. Once you’ve done that, or you’re focusing on your file that’s never opened, clicked or converted, send a re-activation campaign. Let them know that unless they complete the required step, typically clicking on a link within the email, that you’ll never email them again. This not only removes disengaged subscribers from your file, but it will also remove spam traps.

If you’re only worried about isolating spam traps, you can segment your file based on activity and source and use multiple IP addresses to mail off of. Use spam trap reporting, like your Certified reports of Microsoft’s SNDS, to determine if you hit a spam trap. If you’ve identified a segment with a spam trap, you can decide to drop that particular segment or send a re-activation campaign to remove the trap hits. This can be a long and arduous process, but it can reduce the number of addresses you have to purge from your file, and it sure beats shooting them in the head.

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