email marketing best practices say keep fake emails off your list and fake flamingos off your lawnKeeping your in-house email list relevant and clean is important. For one thing, a clean list helps your email deliverability rate by decreasing your chances of hard bounces, and therefore list hygiene should also be among your email marketing best practices.

Part of this hygiene is removing those email addresses that haven’t opened or in any way engaged with your messages. Many suggest only sending to subscribers who have engaged within the last 12 months. Some suggest removing any subscriber who hasn’t opened or clicked within the last 6 months. You’ll know which of these guidelines works best for your own internal email marketing best practices.

But what do you do about the subscribers who will never engage because they aren’t real subscribers in the first place?

A new client of our email marketing agency has been sending us a compiled list of weekly subscribers from their website so we can manually send out a Welcome email on their behalf. This week, we had a 30% hard bounce rate with their list of new subscribers! Looking into the reporting, the primary bounce reason was “User Unknown” with the description “Address is non-existent at the domain.” (Note that this is a big deal because a 30% hard bounce rate is very bad for your email deliverability!)

Many of these bounces had the domain of Mind you, this company is both a brick-and-mortar store with 60+ locations on the East Coast, and an online presence. So it’s not unrealistic for them to have British customers, but these hard bounces indicate that these email addresses may have been, for reasons unknown, added to their system by a piece of malicious software. And to have 30% of the new subscribers suddenly come from the UK was unusual. For them, we recommend email marketing best practices that include one of the techniques mentioned below to prevent these kinds of malicious fake subscribers in the future.

In another example, a tech company client based here in Silicon Valley began sending emails every time they added a new blog post. Whoever wanted to receive the blog emails simply added themselves to their sign-up page. After 6 months or so, they started seeing a tremendous increase in emails sent and subsequently their monthly bill for emails sent went through the roof (because some ESP pricing is based on numbers of sends).

It turned out a lot of random email addresses (many of them and which are typically used for personal email accounts, not business) were added to their blog email subscriber list. Ordinarily, this wouldn’t set off any flags, but the company’s business model is B2B, providing advances in hardware and software to other manufacturers. So the bulk of their email list is made up of corporate email addresses, not personal ones. As soon as we realized all these personal email addresses had been added, they added a CAPTCHA to their sign-up page, and the number of personal emails added to their blog post list decreased dramatically.

As for the ones still on their list, we suggested that they “temporarily” remove the questionable email addresses by segmenting them and sending a double opt-in email to them. This was necessary as these email addresses never bounced, so the ESP’s automated thresholds on stopping those sends were never met. (Note: Double opt-in is another of the email marketing best practices you’ll find below that can help prevent your list from being compromised.)

It’s uncertain why these clients were targeted with random email addresses added to their mailing lists. Was it a bot programmed by a teenage hacker as a proof-of-concept? Were they trying to overload their servers?

Regardless of the reasons, it’s important to keep your lists clean, and it begins on Day 1. If you haven’t yet established email marketing best practices to protect your list, there are many ways to accomplish this, including:

  • A double opt-in email sign-up process to confirm subscription
  • An email verification service such as BriteVerify or Email Answers (both ClickMail partners…please contact us to find out which solution better fits your needs)
  • A strict threshold on bounces

If you want to protect yourself, your reputation and your budget from these kinds of malicious attacks on your in-house email list, talk to our email marketing agency.

Published On: April 8th, 2014Categories: Email deliverability, Email marketing best practices

About the Author: Sharon

Sharon Ernst from is on a mission to improve the business and marketing writing skills of today’s workforce with her blog, newsletter and online classes. Her newest class on intermediate email copywriting covers 19 tips and techniques non-copywriters can put to use right away for better results. The class has real-life examples and before/after comparisons to make the lessons stick. Find her class at When she’s not busy helping employees, managers and marketers master their writing skills, she and her husband are busy raising pigs, cows, chickens and vegetables on their 20-acre farm.

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