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Email Validation Services vs Traditional List Cleaning

Email address validation services are a popular option for cleaning a marketing list, but how do they work, how are they different from traditional list cleaning methods, and how do the results stack up? Let’s pull back the curtain and find out.

Hi, Do You Validate?

Email address validation services are an attractive, simple concept: send over your marketing list, and they’ll tell you which email addresses are bad. While this is a seemingly easy way to clean your list, how validation services identify bad addresses might change your perspective on how valuable those services are. Typically, they’ll provide some sort of risk assessment for each address through a couple of methods:

  1. Checking it against their existing database of known bad addresses (e.g. invalid addresses, spam traps) and known risk factors (e.g. role accounts, common typos)
  2. Testing the validity of any remaining addresses by opening a connection with the recipient’s email server directly as if they are going to send an email to the address in question. The server’s responses translate to roughly “Sorry, that address doesn’t exist”, in which case they’ve learned that the address is invalid, or “Sure, go ahead and send the email”, in which case they assume that the address is good.

While these methods will help you identify and remove some invalid or high-risk addresses, they are inherently flawed because they assume validity based on lack of negative indicators: 

“Is the address on our existing list of bad addresses? No. Does it bounce when we try to send to it? No. Then it must be valid.” 

This is important because spam traps are kept secret by design, and new traps are created all the time. The traps that are known to the validation service are just the tip of the iceberg, so the spam traps that they don’t flag would still be on your list.  Additionally, some domains will accept email for any address regardless of if it exists or not. To be fair, validation services will usually flag these addresses as “catchall” domains so at least you’re aware, but in the end, the test result is still undetermined and those addresses have been neither validated nor invalidated.

The biggest limitation though is in the implications of validation itself. Many marketers may assume that a validated list is one that is ready to send to: You send in a dirty list, and get back a clean one, good to go. What you really get back is a list divided into a few categories:

  • Bad/Invalid Addresses: You shouldn’t send emails to them at all.
  • Valid Addresses: They will accept the email. Some may have risk factors attached that will allow you to parse them out further depending on your risk tolerance.
  • Undetermined Addresses: These might be valid, but you’ll have to decide what to do with them.

Even if you choose the safest route forward and only send to the valid addresses with no risk factors attached, those addresses can still be spam traps, and they can still generate spam complaints (e.g. if you’re sending without explicit permission). The point is that “valid” is not the same as “safe”, and validation services cannot account for permission, nor for the spam traps they don’t know about. At a minimum, validation services can usually identify some addresses that you should not send to, and some that are risky, and there is value in that, though it’s important not to come away with a false sense of security about the safety of your list.

The Old Fashioned Way

The purpose of list cleaning is to protect your sender reputation not just from the invalid addresses on your list, but from spam complaints and spam traps too, reducing as much potential damage as possible from a list-risk perspective. In order to achieve this, traditional list cleaning uses the inverse of the methods employed by validation services. Instead of identifying and removing known bad addresses, the goal is to identify and keep only known good addresses, discarding all others:

  1. Remove any addresses that have not provided explicit permission for marketing and other high-risk addresses (e.g. role accounts).
  2. Remove any unengaged addresses (those that have not opened or clicked in 6+ months or less, depending on your sending frequency)

Notice that in contrast to validation services, this method tests for more than just validity, and relies on the presence of positive indicators to determine whether an address is safe:

“Did the recipient provide explicit permission? Yes. Have they also engaged recently, indicating a real and interested human still exists behind the address? Yes. Then it’s not only valid, it’s also safe to send to.”

The result is a clean list that won’t contain any hard bounces or spam traps, and won’t generate spam complaints (at least for permission-related issues). That’s much better than validation services can offer, and at no cost, so in most cases it’s the preferred method. It does make sense to use validation in some cases, for example, where you have permission, yet lack recent engagement data to properly perform list hygiene. It’s less effective, but it’s better than nothing.  Not all list cleaning scenarios are simple, so for help navigating the grayer areas, refer to this article on What To Do With An Old Marketing List.

About the author

Jake Hoiby is an email deliverability expert that manages email systems, sender reputation and user compliance. He teaches small businesses how to avoid common pitfalls of email marketing and ensure their email reaches the inbox. In his spare time you’ll find him building, automating and tinkering with just about everything.