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Email List Hygiene: How to Build a Clean Email List


Internet service providers (ISPs) take many things into consideration when deciding if your email will reach the inbox or not. One of these considerations is subscriber engagement.

How interested your subscribers are in your content and sending frequency both play a role in subscriber engagement. Another crucial component of having an engaged list is having a list that is comprised of active, valid email addresses.

If you aren’t sending to real email addresses, then there is no opportunity for someone to engage or interact with your campaign. And, more importantly, it’s a red flag to ISPs about your mailing practices.

Matt McFee, BriteVerify

So, how do you build an email list of valid email addresses?

Matt McFee, CEO & Founding Partner of BriteVerify, a provider of email verification solutions, shared insights with us on building a valid email list, as well as list hygiene tips for keeping only valid, engaged subscribers on your list. Here’s what he had to say.


What are inactive and invalid email addresses? What is the difference between the two? Should they be treated differently?

Inactive email addresses are emails that have not opened or clicked on campaigns sent from a specific marketer over a defined period of time. Marketers often try to re-engage inactives using special offers or a funny break-up email.

Others will ask the inactives if they’d like to change the frequency of emails to better fit their needs. While the risk associated with sending to inactive emails is debated, most feel it’s important to address inactive emails separately from the active ones.

Invalid emails are addresses that don’t exist and will bounce when delivered. A few bounces shouldn’t affect deliverability, but too many will eventually make it difficult to reach the inbox. For this reason, most companies prefer to remove invalid emails from their lists before their next campaign.

While verification is not a silver bullet for all delivery issues, it will reduce or eliminate delivery problems associated with invalid emails.

What are the main reasons an email address is invalid?

Emails can be invalid for a few reasons:

  • Bad Format: Email addresses have a simple format of accountname@domainname.suffix. If any of these elements are missing or duplicated, then it is not a valid email address.
  • Bad Domain: If the format is correct but the domain name doesn’t have an email server associated with it (ex. accountname@noemailserverhere.suffix) the address is invalid because there is no email server to receive messages sent to it.
  • Bad Account: The third kind of invalid email is an address that contains an account name that doesn’t exist at the domain associated with the address (badaccountname@gooddomain.suffix).

All of the above invalid email types will be identified as invalid through a list verification process.

What impact can invalid email addresses have on your email campaign?

Data quality is one variable ISPs look at when deciding what to do with your emails. If an email list is clean of invalid data, and other variables like IP reputation, content, and engagement are strong, an email message is likely to reach the inbox. However, as the quality of an email list worsens, the likelihood of that message being junk-mailed or blocked altogether increases.

What are the warning signs of a “bad” email list?

When it comes to email verification, the most visible indication of a bad list is the invalid rate. However, even after invalid emails are removed from a list, there are still noticeable indicators of list quality. A list containing too many role addresses (info@, sales@…) or a meaningful number of old domains (remember can indicate poor quality.

Mailing to a bad, but valid, list of emails will generally result in severely underperforming campaigns, a spike in complaint rates, and possible blacklisting due to the existence of spam traps.


Which email address acquisition methods are more likely to result in invalid email addresses?

Point-of sale email collection often yields a higher than average invalid rate due to the nature of the process (buyer speaks, clerk listens, then types). Mobile devices generate higher than normal invalid rates as virtual keyboards and autocorrect tend to increase mistakes.

We also see a correlation between the perceived value of an offer and the associated invalid rate. Our assumption is that human nature causes people to be extra careful when they really want to take advantage of the offer. Conversely, people tend to pay less attention and make more mistakes if they don’t care that much about the offer they’re signing up for.

What are some ways you can build a valid email list?

A vast majority of today’s marketers attract visitors to their websites using some combination of online and offline marketing. Converting visitors to subscribers by offering something of value (e.g., discount, white paper) in exchange for contact information (e.g., email, name) is probably the most common method of building a good email list.

You may have also seen business card fish bowls in restaurants, have been asked for your email when buying something in a retail store, or have handed your card to a vendor at a trade show. These off-line collection methods are used by marketers to supplement their online list building efforts.

Unfortunately, some marketers take short cuts and purchase email lists, assuming the lists will contain valid emails and deliver great value. This method of ‘list-building’ typically creates more headaches than it cures and should be avoided at all costs.

What tactics should you use during the signup process to ensure that your list is only comprised of valid email addresses?

In-form verification tools like BriteForms do a great job of ensuring that typo mistakes get corrected. BriteForms also helps identify and block bots and manual form fraud. Web form verification is focused specifically on eliminating typo mistakes before they become lost opportunities.

Some websites will ask for the email address to be entered twice to confirm each entry is the same. While this doesn’t confirm the validity of an email it does confirm that the first email provided matches the second. Since in-form verification has become so easy to install, we’re seeing fewer double email entry forms produced today.

Registration confirmation processes like double opt-in (DOI) or confirmed op-in (COI) are primarily used to confirm a person’s interest in joining a site. The process involves sending an email immediately after a person registers, with a request to click a link to confirm their interest.

Some marketers like this method since the extra step solidifies a person’s intent. But since not all registrants click on the confirmation email, the result of DOI / COI is a reduction in the number of people added to your email programs. For this reason, many marketers do not use DOI.


Which types of actions should lead to people getting removed immediately from your list?

While CAN-SPAM in the U.S. allows for a 10-day deadline for honoring unsubscribes, the ethical thing to do when receiving an unsubscribe request is to remove the person immediately. Hard bounces related to invalid emails should also be removed immediately so they don’t impact deliverability.

Soft bounces are bounces that occur for temporary reasons (server issue, inbox overcapacity). These type of bounces don’t necessarily need immediate attention, but should be monitored closely. If an email address remains a soft bounce for 3 consecutive campaigns or over the course of month, we recommend removing it from all future campaigns.

How do you measure whether your list hygiene and re-engagement campaigns are having a positive impact?

The most obvious indication will be the performance of subsequent campaigns. Delivering cleaner data and properly addressing re-engagement opportunities should yield higher performing campaigns. While many companies define email success differently, most agree that higher open rates, higher click rates, and improved email revenues are indicators of success.

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Lauren Smith

Lauren Smith

Lauren Smith is the VP of Acquisition & Lifecycle Marketing at Litmus