Address validation confirms an email will go to a person, but not whether it’s the right person and that makes a big difference.

There’s been a long debate about single versus double opt-in with, let’s be honest, the single opt-in approach winning out in most cases. We all understand why.

Double opt-ins add friction and inconvenience to the signup process. The harder it is to subscribe, the fewer customers and potential customers will do so. As marketers, we want to minimize barriers and make the customer experience as simple and easy as possible.

The problem with simple and easy is that it’s prone to simple and easy mistakes. Single opt-in, especially when implemented indirectly (for example, by a clerk at point of sale) is prone to typos. While often benign, these can lead to list hygiene problems.

To reduce these issues, many companies have turned to address validation. Ideally performed in real time at point of entry or if not, in bulk after the fact, address validation identifies invalid and undeliverable addresses. Some even purport to identify spamtraps and troublemakers.

This type of validation is extremely useful and, especially when performed in real time, can improve both user experience and list hygiene. But despite these benefits, it is not equivalent to using double opt-in, which addresses two questions while address verification only addresses one.

Address verification answers the question, “Does this email address exist?” Double opt-in also addresses the question, “Is it owned by the person who gave it to me?”

It may seem unlikely that of all the possible ways someone could mistype their address, they would manage to hit upon a valid address owned by someone else. However, this problem is actually quite widespread, but heavily clustered.


The above, anonymized image is from a Facebook conversation between two friends (Read more...) is similar to many others I’ve seen. The problem occurs in crowded name spaces (Gmail, Outlook) and appears to be most common when people have the “normal” address for a range of names.

If you’re John Doe and you have jdoe@gmail.com, you will likely get email for many John Does. You’ll probably also get emails meant for James, Jack, Jane, Janice, Jamilla, and Joan Doe. It’s worth noting that neither of the individuals in this case had common last names; quite the opposite, in fact.

Where this issue matters the most is where it also the least likely to be addressed: transactional messages.

There are three main reasons why transaction messages are the most problematic:

  1. Transactional messages are often the most important to the recipient. They often contain very valuable, even essential information, including shipping confirmations, account updates, return notifications and even electronic delivery of items such as tickets. Failure of a recipient to receive these messages can cause them and the sender big headaches.
  2. Transactional messages often contain highly personal information. In addition to telling third-parties which companies an individual is doing business with, transactional messages often include personal information. In the most extreme cases, they may contain temporary passwords to access online accounts.
  3. Transactional messages often don’t include an unsubscribe mechanism. This is the kicker. Since CAN-SPAM doesn’t require unsubscription links in transactional messages, many organizations elect not to include them. To compound the problem, it is also not uncommon for notifications related to purchases and accounts to require a login in order to modify preferences. Obviously, the actual recipients don’t have the login details to do this.

One solution to these problems is to use confirmed, or double, opt-ins. But for many, the increased friction and inconvenience for the majority are seen to outweigh the benefits for the minority. Another solution is to offer an unsubscription in every message, even the transactional ones.


The best option, though, is a “this is not me” (TINM) button. Implementing a TINM solution is more complex, as it typically requires new site functionality, but it’s being used by a growing number of senders, including Twitter, as seen above.

As electronic delivery of important and valuable documents, services and products grows, so does the need to ensure not only that the content is delivered to an address, but to the right address. Next time you’re reviewing your unsubscription and preference options, don’t forget the unintended recipient use case.

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