Email list decay: inevitable but not necessarily bad

by | Jun 7, 2017 | Email Marketing & Automation | 0 comments

Marketers and salespeople work hard to earn email addresses from prospects and leads with whom they’d like to communicate in order to educate them and to stay connected with them through their buying journey.

Plus, it feels good to see a list grow and thrive, especially if it has been cultivated organically and through efforts designed to attract engaged readers. Unfortunately, not all the names in a contact database remain valid as time goes on.

List Decay

Email addresses in a contact database can become “bad” for a few reasons:

  • A contact has changed jobs and their email address has changed
  • A contact has stopped using or cancelled their email account (think AOL or Earthlink)
  • A company had gone out of business or changed names
  • A contact simply stopped using an email address and stopped logging in, triggering the email service provider to deactivate the account
  • An ISP flagged a sender as a spammer

This atrophy is known as list degradation or list decay (or if you like the Walking Dead, maybe you prefer “list rot”). Whatever you call it, it’s important to know that your list needs to be consistently supplied with new email addresses in order to counter its natural decay.

Marketing databases typically decay at 22.5% per year or about 2% per month. If no new contacts are added, eventually, a contact list would have no valid email addresses and become a dead and worthless asset.

Now, we can’t do a lot about the rate of decay especially when it is related to user behavior such as closing or changing an email address. What we can do is make sure the list continues to grow, reduce unsubscribes and improve engagement.

List Cleaning

Emails that have become invalid can affect a couple key metrics: bounce rate and deliverability. High bounce rates and low deliverability rates can diminish the sender’s reputation and score which can ultimately lead to the sender being labeled as a spammer, making it even harder to reach valid subscribers. Keeping bounce rates low and improving deliverability is vital to email marketing and inbound marketing success.

Removing bounced or ineligible email address from a list helps keep the list clean. Even better, keep these emails on a suppression list to ensure they are not inadvertently added or re-imported to your contact or email database.

In addition to bounced email addresses, removing unengaged contacts over time allows email marketers to mitigate against spam reports.

Mailchimp applies “member ratings” for each contact in an account’s contact list. Utilizing open rates, click rates and sending frequency, Mailchimp weighs contact activity. Member ratings can be used to create segmented mailing lists for email campaigns, especially reengagement campaigns designed to improve list health and data integrity or to suppress emails to un-engaged recipients.

List Growth

Not only should marketers evaluate list decay, bounces, unsubscribes and reader engagement, they should analyze list growth.

Take notice of lists which, though continuing to grow, grow at a declining rate. This decline could indicate a problem with efforts related to converting first time contacts, form and landing page optimization and contact retention.

To calculate the rate of growth (or decline), subtract the number of unsubscribes from the number of new subscribers, divide that number by the total number of email addresses in the list and then multiply by 100.

(100 new subscribers – 10 unsubscribes/abuse reports)÷17000 email addresses * 100 = .53% list growth rate

In the above example, the rate of growth does not outperform the rate of decay (monthly or yearly). A good goal, at minimum, it to grow the number of email addresses in your database by at least the rate of decay. But be wary of extraordinary growth. This could indicate bots are completing your forms or addresses are being added for users who did not opt-in.


Decay is inevitable. But it isn’t necessarily a bad thing. Losing invalid email addresses or reducing unengaged users allows you to focus your efforts on those mostly likely to convert or take action.

And remember, especially with multichannel strategies, that list decay doesn’t just apply to email. Whenever someone un-follows you on Twitter or un-likes your Facebook page, you have experienced list decay.

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