How do email verification services help identify high-risk addresses?

Email verification services analyze email addresses for various factors, including syntax errors, domain validity, mailbox existence, and known spam traps . They classify addresses into categories like valid, invalid, risky, or unknown, providing data to help you decide which addresses to keep or remove, thereby protecting your sender reputation.

What is the main difference between a hard bounce and a soft bounce?

A hard bounce indicates a permanent delivery failure, such as an invalid or non-existent email address, and these should be removed immediately. A soft bounce is a temporary delivery issue, like a full inbox or server problem, which might resolve itself. While soft bounces can sometimes be retried, consistent soft bounces can also indicate a high-risk address.

Why is a re-engagement campaign important before deleting inactive subscribers?

A re-engagement campaign provides a final opportunity for inactive subscribers to indicate their continued interest. If they respond, they can remain on your list. If they don't, it confirms their disengagement, providing strong justification for removal. This process minimizes the risk of sending to unwanted addresses, which can lead to spam complaints and damage your sender reputation.

How often should I clean my email list?

The frequency of list cleaning depends on your list acquisition methods and how quickly your list accumulates high-risk addresses. For actively growing lists, a quarterly or semi-annual cleanup is advisable. However, continuous monitoring of bounce rates, complaints, and engagement metrics within your ESP allows for more agile and prioritized list cleaning .

What are the signs that my sender reputation is suffering?

Signs of a suffering sender reputation include increasing bounce rates (especially hard bounces), rising spam complaint rates, a decline in open or click-through rates, and your emails consistently landing in spam folders. Mailbox providers might also throttle your sending or even blocklist your domain or IP. Regular monitoring with tools like Google Postmaster Tools can provide valuable insights into your reputation.

How to identify high risk email addresses to delete from my ESP? - Sender reputation - Email deliverability - Knowledge base

Managing a large email list can be challenging, especially when you inherit a database without a strict double opt-in process. The goal is often to clean out addresses that no longer serve a purpose, but proving the necessity of deletion to stakeholders can be difficult. We need to identify high-risk email addresses to remove them from our ESP, improving deliverability and protecting our sender reputation.

Many of us grapple with extensive lists, some with millions of users who signed up years ago but are no longer active in the product or engaging with our emails. Sending to these addresses can harm our email program by increasing bounce rates, spam complaints, and reducing overall engagement. These metrics directly influence how mailbox providers view our sending practices, potentially leading to emails landing in spam folders or, worse, our domain or IP address being placed on a blocklist (or blacklist).

The primary objective is often to enhance deliverability and maintain a strong sender reputation. This involves strategically identifying and removing problematic addresses. It's not just about removing invalid emails, but also about understanding which segments pose the highest risk and can be safely removed or re-engaged.

Understanding high-risk email addresses

To effectively identify high-risk email addresses, it's crucial to understand the different categories they fall into and why they pose a threat. These addresses aren't just 'invalid,' but span a spectrum of issues that can cumulatively degrade your sending reputation and lead to your emails being marked as spam or your domain appearing on an email blacklist. Understanding these types is the first step in effective list hygiene.

Beyond simple invalid addresses (those that don't exist), you'll encounter spam traps (or honeypots), which are email addresses specifically designed to catch spammers. Sending to them indicates poor list acquisition practices. Additionally, there are recycled email addresses, which were once valid but have become dormant and are then repurposed by mailbox providers, sometimes into spam traps. Continuing to send to these can lead to bounces or, more severely, spam complaints.

Other high-risk categories include 'catch-all' addresses, which accept all mail for a domain but can hide many invalid users, and 'disposable' email addresses, often used for one-time sign-ups to avoid marketing emails. Engaging with users who provide these types of addresses suggests low intent and can inflate your list with unengaged contacts. For a more detailed breakdown of risky email types, you can refer to Verifalia's guide on risky email types. Each of these address types, if not managed, contributes to a decline in your sender reputation and risks placement on a blocklist.

Category	Description	Impact on deliverability
Invalid/Non-existent	Addresses that do not exist or are no longer active.	High hard bounce rates, signaling poor list quality.
Spam traps	Honeypots set up to identify spammers. No legitimate subscriber would opt-in.	Immediate damage to sender reputation, leading to blocklisting (or blacklisting).
Recycled addresses	Former active addresses that become inactive and are later reactivated or turned into spam traps by mailbox providers.	Can result in hard bounces or, if turned into a spam trap, blocklisting (or blacklisting).
Disposable emails	Temporary email addresses used for short-term sign-ups.	Low engagement, high unsubscribe rates, and potential for spam complaints.
Typo domains	Email addresses with common typos, such as @gmial.com or @hotmaill.com.	Leads to hard bounces or, if the typo domain is a spam trap, immediate reputation damage.

Identifying risky segments in your ESP

Identifying these risky segments within your ESP involves analyzing various data points. Start by leveraging your ESP's reporting features to pinpoint addresses generating hard bounces. These are immediate indicators of invalid or non-existent email addresses and should be removed promptly, as they directly impact your deliverability rates.

Next, examine engagement metrics. Look for subscribers who haven't opened or clicked an email in a significant period, perhaps 6 months to a year, or even longer for very old lists. These inactive users can turn into recycled addresses or spam traps over time. Pay close attention to contacts who have never opened an email, especially if they also show bounce activity or were acquired a long time ago. These are prime candidates for removal or a targeted re-engagement attempt.

Finally, consider the age of the subscriber and their last activity with your product or website, not just email engagement. A user who created an account six years ago and hasn't logged in for two years, alongside never opening an email, presents a clear high-risk profile. Segmenting your list based on these combined factors—bounces, email engagement, and product activity—will help you create targeted groups for verification and cleanup.

Identifying risky segments

Focus on segments with clear signs of low quality:

Hard bounces: Emails that permanently fail to deliver. Remove them immediately. Your ESP should automatically suppress these.
No engagement (email): Subscribers who have not opened or clicked any email in a long time (e.g., 12+ months). Consider these for re-engagement or removal. Find out the risk of sending to inactive users.
No engagement (product/site): Accounts created long ago with no recent login or activity, coupled with no email engagement.
Spam complaints: Emails that users have marked as spam. Your ESP should suppress these, but actively review these lists.

Prioritizing segments for verification

To gain buy-in for deletions, start with the 'worst' segments to clearly demonstrate the problem:

Bounced, never opened, and not suppressed: These are likely invalid and are still taking up space.
Bounced, never opened, and very old: Emails that have shown no engagement or deliverability for over 365 days, or even multiple years.
Inactive and old accounts: Subscribers with account creation dates exceeding five years and no recent activity.

Executing the cleanup and re-engagement

Once you have identified your high-risk segments, the next step is to use an email verification service. This service can accurately tell you which email addresses are truly invalid, risky (like spam traps), or safe to email. After verification, you'll have solid data to present as justification for deletion. Suppressed emails, such as hard bounces, can often be deleted directly from your ESP without external verification, as their undeliverable status is already confirmed.

For segments that are old but don't immediately appear invalid, consider a re-engagement campaign. This allows you to attempt to reactivate these users one last time. Send a last goodbye email or a series of emails with clear calls to action, asking them to confirm their interest or update their preferences. Those who don't respond can then be safely removed. It's crucial to implement this slowly, starting with your most engaged older segments and gradually moving to less engaged ones to monitor the impact on your sender reputation.

After the cleanup, implement preventative measures like double opt-in for all new sign-ups. This ensures that new email addresses are verified and engaged from the start, significantly reducing the influx of high-risk addresses into your list. Regular list hygiene is an ongoing process, not a one-time fix. Consistently monitoring your email deliverability metrics, like open rates, click-through rates, and bounce rates, will help you maintain a healthy list. You can run a deliverability test periodically to check on the health of your email program.

SQL queries for identifying high-risk segmentsSQL

/* Example of a high-risk segment for deletion */
SELECT email_address
FROM your_email_list
WHERE last_email_opened_date < '2023-01-01'
  AND last_product_login_date < '2023-01-01'
  AND hard_bounce_count > 0
  AND is_suppressed = FALSE;

/* Example of a re-engagement segment */
SELECT email_address
FROM your_email_list
WHERE last_email_opened_date BETWEEN '2023-01-01' AND '2023-06-30'
  AND last_product_login_date < '2023-07-01';

Ongoing list hygiene and prevention

Maintaining a healthy email list is an ongoing effort that requires continuous monitoring and proactive measures. Regularly cleaning your list of high-risk email addresses prevents accumulated problems like low engagement and high complaint rates from negatively impacting your sender reputation. A clean list ensures your emails reach engaged recipients, improving overall campaign performance and return on investment.

Beyond regular cleanups, establishing robust acquisition practices, such as preventing fake email addresses, is vital. Proactive steps, like implementing confirmed opt-in (double opt-in), are invaluable for preventing risky addresses from entering your database in the first place. You can also monitor for blocklist (or blacklist) listings to quickly address any reputation issues. This integrated approach, combining cleanup with prevention, is key to sustainable email deliverability.

Key takeaways

Systematically identifying and removing high-risk email addresses from your ESP is not just a best practice, it's essential for maintaining a strong sender reputation and ensuring your messages consistently reach the inbox. It requires a combination of robust data analysis, strategic segmentation, and leveraging the right tools. By taking a proactive approach, you can significantly improve your email program's performance and prevent future deliverability issues.

The process may involve internal challenges, especially when advocating for list reductions, but the long-term benefits of a clean, engaged email list far outweigh the initial effort. By focusing on the most problematic segments first and demonstrating tangible improvements in your email metrics, you build a compelling case for ongoing list hygiene. Prioritizing quality over quantity will ultimately lead to higher engagement, better deliverability, and a stronger connection with your truly interested audience. For further guidance, explore M3AAWG's sending best practices.

Views from the trenches

Best practices

Actively monitor your ESP's bounce reports and immediately suppress or remove hard bounce addresses to protect your sender reputation.

Segment your email list based on inactivity across both email engagement and product usage for a comprehensive view of risky contacts.

Utilize email verification services on older, unengaged segments to validate addresses before attempting re-engagement or deletion.

Implement a double opt-in process for all new sign-ups to ensure high-quality, engaged subscribers from the outset.

Conduct re-engagement campaigns for moderately inactive segments, offering a clear path to stay subscribed or opt-out gracefully.

Common pitfalls

Hesitating to delete inactive or problematic email addresses due to concerns about list size, despite the negative impact on deliverability.

Failing to implement a double opt-in, allowing invalid or low-quality email addresses to enter your list continuously.

Not regularly monitoring ESP metrics like complaint rates and engagement, missing early signs of declining list health.

Sending re-engagement campaigns too broadly or aggressively, potentially triggering spam complaints from disengaged users.

Ignoring email addresses that generate soft bounces, as these can indicate temporary issues that may become permanent problems if unaddressed.

Expert tips

When dealing with very old lists, focus on proving that emails are no longer in use to justify deletion to internal stakeholders.

If an email verification tool indicates that old addresses are still 'valid,' but engagement is non-existent, remember that validity doesn't equal engagement or interest.

Consider the business goal behind cleaning your list, whether it's mail volume, sales, or deliverability, as this guides your strategy.

Clean data cleanup is a process of tradeoffs, weighing the risks, costs, and benefits of keeping or removing different segments.

For mandated legal notifications, work closely with your email service provider to ensure proper setup, alert postmasters, and manage sending rates.

Marketer view

Marketer from Email Geeks says to remove inactive email addresses and create segments to send a 'last goodbye email' with an option to opt out, especially for very large lists where many users are no longer active in the product.

2022-05-10 - Email Geeks

Expert view

Expert from Email Geeks says that the underlying issue with old, unengaged addresses is the potential for recipients to react in ways that tell machine learning filters the mail is unwanted, which can significantly tank delivery.

2022-05-10 - Email Geeks