Attack of the Email Zombies


Think back to the first time you sent an email. Do you remember what your first email address was? Studies have shown that 30% of subscribers change email addresses annually and 17% create a new email address every six months, so it’s pretty likely that you’ve had your fair share of email addresses over the years.

Recently, while troubleshooting some email rendering problems with a particular ISP, I remembered that I once had an email account with them. Though I hadn’t used the email address in nearly a decade, I logged in to find my account just as I had left it 8 years prior.

To my surprise, my abandoned address hadn’t been revoked and re-issued, nor had it become a wasteland for spammers. Although there were a few pieces of spam buried in the midst of the 3,000+ unread emails, I noticed something even more disturbing: I had become an email zombie. The inbox was filled with marketing messages from major brands I hadn’t interacted with in nearly a decade. After more than 8 years of ignoring their advances, you’d think that they would’ve taken the hint and dropped me from their lists.

The Impact of Zombies

A zombie is an email subscriber on your list who has a valid email address but who has not opened any of your emails for an extended period time, often because the subscriber has changed their email address and abandoned their old email account.

It’s essential that you purge your list of zombies as often as possible. Since many email platforms (ESPs) charge per email, sending to a zombie is like sending money into a black hole. You’re wasting your time and financial resources marketing to someone who isn’t there. If you’re lucky, the customer reengaged with your brand from their new email address, but either way, if a subscriber hasn’t opened any of your messages in more than a few months, it’s time to cut your losses and move on.

In addition to the direct cost, there’s a secondary cost of zombie infestation and is much harder to recover from. The presence of zombies on your lists can indicate to ISPs that you are not exercising good list hygiene practices. If an ISP finds out that you’re sending to zombies, it will almost certainty have a very negative impact on your sender reputation and deliverability. The worse your reputation, the harder it will be to get you messages into the inboxes of your legitimate subscribers. Think of it as the zombie domino effect; the more you ignore the zombies, the worse your deliverability gets.

Worse yet, ISPs will sometimes actually reclaim email addresses that have been abandoned and use them as honeypots. The ISPs will take possession of the deserted email accounts and, instead of bouncing inbound messages as you would expect, they will monitor to see if anyone is sending to them. Since the email address hadn’t been used by a legitimate subscriber for an extended period of time (usually 6 months or more), ISPs then assume that anyone messaging the account is in violation of basic list hygiene practices and is, thus, a spammer (gasp!).

If you find yourself in this situation, it won’t take long for you to find out that you’ve hit the honeypot spam trap. Once you do, you can expect a long and uphill battle with the ISP trying to clear your name and reputation as a spammer and get your messages delivered.

And though the ISPs aren’t nice enough to tell you that you’ve hit a spam trap, you can usually tell when you start seeing a dramatic decrease in delivery rates and your messages begin getting deferred or even blocked by the ISP.

The best (and only) way to ensure that you maintain a solid sending reputation is to keep a clean, updated database. Depending on how often you deploy emails, it is good practice to purge your list of inactive subscribers at least once a month. A good starting point is to remove any subscribers who haven’t opened your email in the past 4-6 months and adjust based on your company’s sending habits. If you deploy emails on a daily basis, you might use 2-4 weeks as your cut-off.

If while reading this you realise that you have never scrubbed your list for unengaged subscribers, don’t panic. Take the time now to review your list hygiene practices and ensure that you’ll never fall victim to a zombie attack against your brand.

Image: CC0 via Pixabay