What is the typical percentage of 'bad' domains or email addresses in a new signup list?

While there's no single universal percentage, industry observations suggest that anywhere from 5% to over 20% of email list signups can be problematic due to typos, invalid domains, bots, or temporary email addresses. Lists also naturally degrade by about 20% annually.

How do bad domains and email addresses impact email deliverability?

Bad domains and email addresses lead to high bounce rates, which damage your sender reputation with ISPs. This can result in emails going to spam folders or your domain being added to a blocklist (or blacklist), ultimately reducing your email deliverability and wasting resources.

What are the primary best practices for ensuring email list data cleanliness?

Best practices include implementing real-time email validation on all signup forms, using double opt-in, regularly monitoring bounce rates and engagement metrics, and periodically scrubbing your list with a professional email verification service.

What does email list cleaning involve, and why is it important?

Email list cleaning is the process of removing invalid, inactive, unengaged, or otherwise problematic email addresses from your subscriber list. It improves deliverability, engagement metrics, and protects your sender reputation.

Is double opt-in enough to ensure email list cleanliness?

While helpful, double opt-in alone isn't sufficient. Some sophisticated spam traps can click confirmation links, and it doesn't address all forms of list degradation. It should be part of a multi-layered approach that includes real-time validation and ongoing list hygiene.

What percentage of domains in signup lists are bad, and what are the best practices for ensuring data cleanliness? - Sender reputation - Email deliverability - Knowledge base

Maintaining a clean email list is fundamental to successful email deliverability and overall marketing performance. Many organizations struggle with data hygiene, often underestimating the percentage of bad or outdated domains lurking in their signup lists. Understanding the scope of this problem and implementing robust best practices are crucial steps toward ensuring your emails reach their intended recipients and avoid issues like bounces, spam folder placement, or blocklisting.

The impact of dirty data on deliverability

The exact percentage of bad domains in signup lists can vary widely depending on the source of the signups, the industry, and the validation methods in place. However, it's often higher than expected. For instance, in one observation of a large brand's list of 8400 domains, a full 5% were identified as 'bad domains,' including clear typos. This suggests that even reputable organizations can accumulate a significant number of invalid entries without proper front-end validation. More broadly, email lists can degrade by approximately 20% annually due to various factors, including job changes, abandoned accounts, and domain expirations. This natural decay highlights the continuous need for list hygiene.

Bad domains and email addresses lead to various problems, including high bounce rates, which negatively impact your sender reputation. Internet Service Providers (ISPs) view high bounce rates as a signal of poor list quality or potentially spammy sending practices. This can result in your legitimate emails being routed to the spam folder or, in severe cases, your IP address or domain being added to a blocklist (or blacklist). An unhealthy list also inflates your sending costs, as you pay to send emails that will never reach an inbox, wasting resources and diminishing your return on investment.

Beyond deliverability, dirty data undermines the accuracy of your engagement metrics. If a significant portion of your list consists of invalid addresses, your open rates, click-through rates, and conversion rates will be artificially deflated, making it difficult to gauge the true effectiveness of your campaigns. Moreover, sending to invalid addresses can expose you to spam traps, which are email addresses specifically set up by ISPs and anti-spam organizations to identify senders with poor list hygiene. Hitting a spam trap can severely damage your sender reputation and lead to immediate blocklisting. You can learn more about how spam traps work in our detailed guide.

Proactive strategies for clean signups

The most effective way to ensure data cleanliness is to prevent bad data from entering your list in the first place. This requires implementing robust validation processes at the point of signup. Many free and commercial tools are available to help with this. You should always use a trusted validation service and incorporate real-time validation into your sign-up forms. This proactive approach ensures that your list remains healthy from its inception. Find out more about best practices for email validation on signup.

Real-time validation on signup forms can catch common errors such as typos or malformed addresses. This immediate feedback helps users correct their input before submission, reducing the likelihood of invalid data. For example, a simple client-side script can check for basic email format, while server-side validation can perform more complex checks like DNS lookups to verify domain existence.

Basic email validation examplejavascript

function isValidEmail(email) {
  const emailRegex = /^[\w.-]+@([\w-]+\.)+[\w-]{2,4}$/;
  return emailRegex.test(email);
}

While single opt-in is faster for subscriber acquisition, double opt-in adds an extra layer of verification. It requires subscribers to confirm their email address by clicking a link in an initial email. This method drastically reduces the number of invalid or bot-generated addresses, as only genuinely interested users will complete the process. Although it might slightly reduce signup rates, the quality of your list will be significantly higher, leading to better deliverability and engagement.

Reactive list hygiene strategies

Even with strong proactive measures, lists degrade over time. Regular list cleaning is essential to maintain high deliverability. This involves identifying and removing inactive, invalid, or unengaged subscribers. The frequency of cleaning depends on your sending volume and list churn, but a general rule of thumb is to clean your list every six months to once a year. You can get more information on email list cleaning best practices.

One key aspect of reactive hygiene is monitoring your bounce rates. Soft bounces indicate temporary issues, while hard bounces signal permanent delivery failures. Addresses that result in hard bounces should be immediately removed from your list. Many Email Service Providers (ESPs) automatically handle hard bounces, but it is important to be vigilant. Regularly segmenting your list to identify unengaged subscribers can also help; if recipients haven't opened or clicked your emails in a long time, consider re-engagement campaigns or suppressing them from your active sending list.

Here's a comparison of proactive vs. reactive list hygiene:

Proactive hygiene

Focuses on preventing bad data from entering your list.

Real-time validation: Validate email addresses at the point of signup.
Double opt-in: Require subscribers to confirm their subscription.
CAPTCHA: Use tools like Google reCAPTCHA v3 to deter bots and automated signups.

Reactive hygiene

Deals with removing bad data that has already entered your list.

Bounce management: Automatically remove hard bounces and monitor soft bounces.
List scrubbing: Regularly clean your list using an email verification service.
Unengagement segmentation: Identify and segment inactive subscribers, then try to re-engage them.

It's important to remember that double opt-in alone isn't a silver bullet. Some sophisticated spam traps can even click confirmation links. Therefore, a multi-layered approach combining real-time validation, double opt-in, and regular post-acquisition cleaning is the most effective strategy. You can learn more about strategies for email list validation.

Understanding and managing risks

Understanding the types of bad email addresses is key to effective list hygiene. These categories help you prioritize which addresses to remove and what prevention methods to implement.

Type of bad email address	Description	Impact on deliverability
Invalid/non-existent	Addresses that do not exist or are malformed (e.g., typos like @gamil.com, non-existent domains).	Leads to hard bounces, significantly damages sender reputation, and can lead to blacklisting.
Spam traps	Email addresses used by ISPs to identify spammers or senders with poor list hygiene. Never opt-in.	Hitting these leads to immediate and severe damage to reputation, resulting in blocklisting (or blacklisting).
Disposable/temporary	Emails created for short-term use, often to avoid spam (e.g., from Mailinator or TempMail).	Low engagement, increased bounce rates, and can indicate bot activity or uninterested subscribers.
Unengaged/inactive	Subscribers who haven't opened or clicked emails for a prolonged period.	Negatively impacts engagement metrics, signals to ISPs that your content isn't relevant, and can lead to spam folder placement.

Preventing these addresses from reaching your list is paramount. Always use email validation tools at the signup stage. For ongoing list hygiene, regularly check your sender reputation through tools like Google Postmaster Tools. If you see a rise in spam complaints or a dip in engagement, it's a strong indicator that your list might need a deeper cleanse.

Never purchase email lists

Purchased email lists are almost always detrimental to your email marketing efforts. They often contain a high percentage of invalid addresses, spam traps, and unengaged recipients. Sending to such lists can quickly destroy your sender reputation, lead to high bounce rates, and result in your domain or IP being added to a blocklist (or blacklist). Focus on organic list growth through opt-ins instead. Learn more about what happens when your domain is blocklisted.

Monitoring various email blocklists (or blacklists) is a critical component of email deliverability. These lists are databases of IP addresses and domains known to send spam. If your domain or IP address ends up on a prominent blocklist, your emails will likely be rejected by major ISPs. Regular blocklist checking can alert you to issues early, allowing you to take corrective action. An in-depth guide to email blocklists can provide further insights.

Final thoughts on data cleanliness

Ensuring data cleanliness isn't a one-time task, it's an ongoing process that requires continuous attention and adaptation. The digital landscape, including email sending requirements from providers like Microsoft and Yahoo, is constantly evolving. A proactive and reactive approach to list hygiene is critical for maintaining a strong sender reputation and achieving high inbox placement rates.

By actively working to keep your email lists clean, you not only improve your deliverability metrics but also enhance the accuracy of your marketing data, reduce costs, and build stronger relationships with your subscribers. This commitment to data quality translates directly into more effective campaigns and better business outcomes.

Remember, a healthy email list is an asset that fuels your email marketing success. Invest in the right tools and processes to ensure your list remains clean, engaged, and free from problematic addresses.

Views from the trenches

Best practices

Implement real-time email validation at all signup points to prevent invalid addresses from entering your database.

Utilize double opt-in processes for new subscribers to ensure genuine interest and valid email addresses.

Regularly segment your email list to identify and suppress unengaged subscribers, focusing on active recipients.

Monitor bounce rates diligently and automatically remove hard bounces from your list to maintain sender reputation.

Regularly clean your email lists using a reputable email verification service to remove invalid or risky addresses.

Common pitfalls

Relying solely on single opt-in, which allows a higher percentage of invalid or bot-generated signups.

Neglecting to monitor email bounce rates, leading to continued sending to non-existent addresses.

Not regularly segmenting and pruning unengaged subscribers, which can negatively impact overall sender reputation.

Purchasing or renting email lists, which almost always contain spam traps and invalid addresses, harming deliverability.

Failing to adapt to evolving email provider requirements and anti-spam measures, causing deliverability issues.

Expert tips

Consider using CAPTCHA or similar bot-prevention measures on signup forms to deter automated signups and list bombing.

Periodically re-engage inactive subscribers with targeted campaigns before suppressing them to maintain list size while improving quality.

Implement DMARC authentication and monitor reports to identify potential abuse of your domain and ensure proper email authentication.

Continuously analyze your email campaign metrics, especially open rates and spam complaint rates, for early indicators of list health issues.

Understand that list cleaning is an ongoing process, not a one-time event, due to natural list decay.

Expert view

Expert from Email Geeks says a significant percentage of domains in signup lists, potentially around 5%, can be bad, and this is a common issue even for large brands.

2021-08-17 - Email Geeks

Expert view

Expert from Email Geeks says many organizations struggle with data cleanliness, and it's rare to see database structures that enforce perfectly clean data from the start.

2021-08-17 - Email Geeks