Grow, clean, maintain: the importance of email list cleaning for long-term growth

Profile photo of author Maddy Osman
Maddy Osman
19min read
Email marketing
September 13th 2022

333.2 billion. That’s the average number of emails sent and received per day in 2022.

Along with the number of emails, spam is also increasing. According to a 2021 Kaspersky Lab report, 45.56% of emails are spam. That’s why email providers like Gmail and Outlook have advanced spam filters.

So where does that leave email marketers?

First, you need to maintain good deliverability to get into as many inboxes as possible. Maintaining a healthy email list is the only way to secure a path toward your subscribers’ inboxes—and, ultimately, guide them toward purchase.

That means it’s critical to have a well-segmented email list that’s full of engaged subscribers—and free of wrong or fake email addresses and unresponsive users.

If that doesn’t sound like your current email list, don’t worry. You don’t need to scrap your email list and start from scratch. Instead, prune your list with the email list cleaning practices we’ll show you.

Here’s what we’ll cover:

  1. Why is a healthy email list paramount
  2. Growing your email lists
  3. Cleaning your email list
  4. How to clean an email list
  5. Maintaining your email lists

Why is a healthy email list paramount?

Let’s say you successfully build an email list with 10K subscribers. But out of the emails you send, 30% are left unopened, and 20% always bounce.

Yes, 10K is a large number. But if a whopping 50% of the emails you send aren’t reaching anyone, that number isn’t doing you any good. Instead, it’s hurting your email deliverability and email marketing efforts.

Ultimately, it’s better to have a smaller list of more engaged subscribers. You’ll be able to reach their inboxes more effectively—and get your messages across when you need to most.

Let’s examine how an unhealthy email list impacts your email marketing efforts in terms of deliverability, customer relationships, data, and costs.

Sender reputation and deliverability

Email deliverability refers to your ability to get emails to your subscribers when using an email marketing service. After all, sending out emails alone doesn’t guarantee a smooth journey from the email server to the recipient’s inbox.

When you send an email, there are a few possible outcomes:

  • The email bounces from the recipient’s email server.
  • The email provider blocks the email or marks it as spam.
  • The email arrives in the recipient’s inbox.

The good news is whether your marketing emails reach their destination isn’t random—it depends on your sender reputation.

If you have a good sender reputation, the email provider considers you a trustworthy sender and places your email in the recipient’s inbox. The lower your sender reputation, the higher the likelihood your emails end up in the spam folder.

Email providers usually calculate a sender’s reputation based on:

  • Emails bounced (hard or soft)
  • Spam complaints from recipients
  • Past unsubscribes
  • Whether the sender sends emails to spam traps

How poor email list hygiene affects deliverability rate

Let’s go back to the 10K subscriber email list example and say that a significant part of it consists of invalid or unengaged recipients.

Here’s what may happen when you send emails to that list:

  • Hard bounces: The destination mail server rejects the email if the email address is invalid or doesn’t exist anymore.
  • Spam folder placement: The recipient finds the email annoying and marks the email as spam.
  • Unsubscriptions: The recipient doesn’t find the email interesting and unsubscribes from the list.

As mentioned, hard bounces, spam complaints, and unsubscribes have one thing in common: They negatively impact a sender’s reputation.

Based on these factors, email providers can decide to blocklist senders. That means their emails won’t even reach the inboxes of engaged customers within that email provider. This is a harsh outcome considering the senders could’ve avoided it by simply cleaning their email list.

Email list cleaning, also known as email scrubbing, removes invalid, irrelevant, or disengaged emails from your list. That way, they don’t affect your ability to deliver emails to your most engaged customers.

Weak customer relationships can harm your list

Subscribers who signed up for your email list may lose interest in the long term or move away from your brand.

Whether they found another business to buy from, didn’t love your product, or just don’t enjoy your emails, it’s important to realize that not every customer is going to be a loyal customer—and then relieve them of their time on your email list.

When you don’t clean your email list regularly, you’re more likely to keep sending emails to these unengaged recipients. That can have many adverse effects, including:

  • Recipients mark your emails as spam or unsubscribe—goodbye, sender’s reputation.
  • Recipients get annoyed—they won’t come back to your brand again.

With email list cleaning, you can move these customers to a separate segment and try to re-engage them. If they still don’t respond, it’s time to say goodbye and remove them altogether.

Accuracy of email marketing campaign results

A large number of unengaged subscribers can skew the value of your email marketing KPIs.

Let’s say your latest email marketing campaign is showing low open and click-through rates. Even if your engaged subscribers respond well to the campaign, you won’t notice it because of the bloated email list.

That isn’t good for accuracy. Worse, you may end up ditching something that works. A clean email list will yield more accurate KPI measurements to help you plan future marketing efforts.

Cost reduction

Most email marketing platforms, including Klaviyo, charge you based on your email volume. So, if you send 10K emails and half of the recipients don’t open them, it’s a waste of money.

A clean email list ensures you spend money on subscribers who are more likely to engage with your emails. Engaged subscribers are more likely to convert, giving you a better return on investment for your email marketing.

In addition, a clean list helps you save on costs related to fixing deliverability issues with ISPs.

Now that you know why having a healthy email list matters, let’s explore how good list growing practices can reduce your email list cleaning efforts.

Growing your email lists

How you grow your email list determines how easy it’ll be to keep it clean. Businesses collect email addresses directly from users using different methods, including:

  • When they sign up for newsletters or any useful content
  • Through a sign-up form on the homepage with incentives and offers
  • Through quizzes and surveys
  • When they sign up for out-of-stock stock notifications
  • When they create an account
  • During check-out
A sign-up form with a discount offer to attract new subscribers.

Source: Color Camp

Although these aren’t the only available methods, they have one thing in common: The customer gets to choose whether you get their email address. Choice is the key word, here.

After all, some businesses buy email addresses in bulk from third parties. While that might sound practical, it isn’t.

Outsourcing your email collection to second and third parties isn’t a great way to grow email lists. It can lead to non-compliance with privacy laws like CAN-SPAM, CASL, and GDPR. Worse, it can have larger damaging implications for your email list:

  • The list may contain fake or disposable email addresses, causing hard bounces.
  • The list’s recipients haven’t given their consent, causing complications that may even lead to lawsuits.
  • The list might include spam traps that’ll hurt your deliverability.

So, how should you walk your way toward email list growth?

Best practices to grow your email list

Let’s look at a few best practices that will help you grow a healthy list while staying compliant with data privacy laws.

Collect Customer-First Data™

Customer-First Data—the combination of zero- and first-party data—is information the customer hands over voluntarily. Unlike third-party data (information you collect indirectly from a variety of sources), Customer-First Data is information you source directly from potential and existing customers.

A few ways to do this include:

  • Through sign-up forms
  • During the account creation process
  • Collecting Customer-First Data during checkout
  • Using surveys or quizzes

Collecting Customer-First Data directly from subscribers ensures you have their consent to email them. It also helps you capture your customers’ interests and use them for email segmentation—so you can send them more relevant messages that make them feel seen.

Use a double opt-in

Following the double opt-in process means sending a confirmation email after a person submits their email address through a sign-up form. That lets subscribers confirm whether they want to be added to the list.

Double opt-in also works as an email validation method to:

  • Weed out fake or invalid email addresses.
  • Remove email addresses with typos.
  • Skip subscribers who only signed up for an offer.

Use acquisition methods that yield quality leads

A common practice for ecommerce brands is to offer shoppers an incentive in exchange for providing their email address and phone number.

Additionally, marketers often use promotions like contests, giveaways, and sweepstakes to grow their email lists. This can be a great way to partner with other brands and expand your reach by offering an incentive to get people to discover your store.

But it shouldn’t be your only strategy, and there’s a reason: The list-building method you use impacts the quality of email addresses you get.

For example, if you offer a discount coupon in exchange for an email address, someone may give away their email address just for that offer. The same goes for any type of giveaway to win products, experiences, or other items of value.

Doing these once in a while is okay, but try not to revolve your entire list-building strategy around this strategy.

Instead, think about trying more sustainable techniques, like:

  • Collecting Customer-First Data through surveys and quizzes
  • Offering relevant content in exchange for contact information, such as a newsletter
  • Promoting experiences that are exclusive to email subscribers, such as first access to new products
  • Implementing a sign-up form with no associated discount

Refining your acquisition methods and the other practices above will help you build a healthy email list.

But even with a solid foundation, your email lists won’t stay healthy forever without proper maintenance.

You need to clean up your email list to ensure long-term success. Let’s see what that looks like.

Cleaning your email lists

Much like everything in life, your email list needs scrubbing from time to time. Overall, the goal during each email list cleaning session is to address:

  • Invalid emails: Some subscribers might delete their email accounts but miss updating their details. Disposable emails may become invalid over time.
  • Duplicate email addresses: You might be sending multiple copies of an email to the same subscriber, increasing your email sending cost and potentially getting on the customer’s nerves.
  • Unengaged subscribers: Some subscribers stop engaging with your marketing emails over time. Maybe they no longer need your products, or maybe they’ve lost interest in your brand.

Beyond that, let’s cover some bases:

How often should you clean your lists?

Remember, list cleaning isn’t a one-time effort. Routinely cleaning your list is the best way to ensure good deliverability.

The frequency with which you clean your list should depend on its size and growth rate. For example, once a year might be sufficient if you have a smaller list (think under 50K contacts), but it’s a good idea to clean your list every 6 months or more if it’s extensive and growing rapidly (think 500K+ contacts).

In general, we suggest cleaning your email list at least once or twice per year, especially before large shopping events when you might expect an influx of new email list subscribers:

  • Black Friday Cyber Monday
  • The holiday season
  • Memorial Day and summer sales
  • Any other major sales event

We also recommend that you do some sweeping after these events to ensure you only added high-quality emails to your list.

Signs that you need to clean your email list

Email list cleaning schedules are great. But you should also pay attention to email performance.

If your email performance KPIs aren’t up to par, you’ll need to sort things out.

Some signs that you need email list cleaning include:

  • Decline in engagement, such as low open and click rates
  • Increase in bounce rates
  • Increase in unsubscribes and spam complaints

Your email marketing platform should be capable of tracking these KPIs for you. Klaviyo, for example, helps you track email deliverability KPIs through campaign trend reports.

Note: Open rates may be inflated for subscribers using the iOS 15 update. If you have subscribers using iOS, consider using only click rate as an engagement metric. If only a fraction of your subscribers is on iOS, you can exclude them from marketing attribution.

How to clean an email list

Now that you know you need to clean up your email list, how do you go about it? Let’s go over how to clean up your email list, step-by-step.

1. Suppress invalid and outdated email addresses

First, you need to identify email addresses that cause hard bounces. Emails to these addresses can’t be delivered for a permanent reason, so it’s best to remove them from your list.

Email list cleaning services and email marketing platforms like Klaviyo help you automatically remove an address on the first instance of a hard bounce.

The next thing to look for is soft bounces. These represent temporary issues with delivering your email and can happen because:

  • The recipient’s inbox is full.
  • The email server is down.
  • The email is too big to be delivered to the inbox.

You don’t need to remove addresses that are soft-bounced immediately. Instead, it’s best to make a protocol for cleaning them.

For example, in Klaviyo, you can automatically suppress an address that soft bounces more than 7x in a row. Klaviyo also provides you with the hard and soft bounce metrics on your campaign trend report.

Bounce metrics on Klaviyo’s campaign trend report.

Source: Klaviyo

2. Identify unengaged profiles in your email list

To recap: Some subscribers might no longer be interested in receiving your emails. But identifying unengaged subscribers isn’t as straightforward as detecting bounced emails—you have to first define a baseline.

The baseline should help you determine the criteria for a person to be considered unengaged. For example, if a person subscribed a week ago and hasn’t engaged with any of your emails, it’s too early to classify them as unengaged.

But if it’s been 3 months, it’s a different story.

With your baseline in hand, you can create segments for unengaged subscribers. For example, here is Klaviyo’s recommended segmenting criteria for engaged subscribers:

Email segments based on engagement

Segment nameCriteriaAction
Never active segmentNo emails opened in the last 180 days No purchases in the last 180 daysSuppress/delete email addresses from the list.
Unengaged, never purchasedAt least one email opened Has clicked on the email at least once No emails opened in the last 180 days Never purchasedSend a sunset email. Suppress/delete email addresses from the list if they don’t respond to the sunset email.
Unengaged, purchased segmentAt least one email opened Has clicked on the email at least once Has purchased at least once No emails opened in the last 180 days No purchases in the last 60 daysSend a re-engagement campaign. Send a sunset email if there’s no response. Suppress/delete email addresses from the list if they don’t respond to the sunset email.

ALT: Engagement-based email segments and cleaning actions.

You can use this as a jumping-off point, and adjust it for your unique business and customer journeys.

3. Try re-engagement email campaigns

Before removing unengaged customers from your email list, you can try winning them back with a win-back email or re-engagement campaign. The campaign can include emails with coupon codes, free shipping, or other offers to entice subscribers to give your business another try. Here’s how SKINN does it:

Example of a re-engagement email

Source: Klaviyo

If the subscriber doesn’t respond to the re-engagement flow, though, it might be time to say goodbye with a sunset flow.

Brands often send sunset flow in two parts:

  • A re-permission email to get the subscriber’s consent again or give them the opportunity to unsubscribe
  • A goodbye email to part ways with the subscriber

Even if they choose to unsubscribe, it’ll be beneficial to you. After all, sunset flows let people unsubscribe rather than mark your email as spam—which is far less damaging to your sender reputation. Here’s the first part of Princess Awesome’s sunset flow:

Example of a sunset email

Source: Princess Awesome

Pro tip: As part of the sunset flow, consider encouraging subscribers to update their preferences rather than unsubscribing completely. This is a great way to reduce the frequency of the email they receive while preserving their contact information.

4. Delete or suppress unengaged profiles

After the re-engagement campaign and sunset flows, you’ll likely win back a few customers. And that’s great—but don’t let it distract you from removing unresponsive subscribers from your email list.

Here are some actions you can take to remove them:

  • Delete unresponsive subscribers from your lists.
  • Suppress unresponsive subscribers from future email campaigns.
  • Create a segment and exclude them from future campaigns.

Maintaining your email lists

Cleaning your email list can make or break your campaigns. But there’s no need for deep dives in the first place if you regularly tend to your email lists.

Here’s what maintaining email list hygiene can look like:

Prioritize engaged subscribers when you send emails

One benefit of email list cleaning is that you’ll get engagement data as a byproduct. You can use that data for creating segments and sending targeted emails to your most engaged customers.

You can also adjust email frequency to less-engaged audiences. That helps ensure your marketing emails don’t annoy low-engaged subscribers and optimizes the cost of sending emails.

Pro tip: Save your biggest and best marketing promotions (like sitewide sales or influencer collaborations) for all your subscribers, while keeping your engaged subscribers in the loop more frequently with consistent brand updates.

Here’s an example of email engagement tracks based on engagement data.

Email tracks based on engagement

Source: Klaviyo

Create additional segments

Email segmentation is an excellent way of keeping customers engaged. You can go beyond email engagement-based segmentation and create segments based on:

  • Demographics
  • Geolocation
  • Purchase history
  • Purchase recency
  • Website engagement
  • Email engagement
  • Predictive analytics

These segments will help you send emails matching your customers’ needs and interests. That lowers their chances of becoming unengaged, which will keep your email list healthy.

Make it easy to unsubscribe

It might be challenging to let go of the subscribers you acquired, but offering an easy unsubscribe option is a smart idea because:

  • It gives you a chance to part with the customer on good terms.
  • It reduces spam complaints that affect your sender reputation.

You can also provide an opt-down option to unsubscribe from your emails selectively.

With Klaviyo, it’s very easy to insert an unsubscribe link into your emails. You just need to add a new unsubscribe tag to your email template.

Add an unsubscribe link in klaviyo

Source: Klaviyo

Continuously analyze performance

After cleaning up the list and making segments, monitor the following email marketing metrics:

  • Email deliverability metrics: bounce rate, unsubscribe rate, and spam rate
  • Campaign engagement metrics: open rate, click rate, and unsubscribe rate
  • Campaign revenue metrics: conversion rate, revenue per recipient, and revenue per campaign

Monitoring your KPIs will help you invest more effort in strategies that work—and pull back on marketing methods that don’t yield results.

Email list cleaning for deliverability and long-term growth

When it comes to email lists, quality matters more than quantity. Even if you have a big email list, what matters is your ability to place your marketing emails in your recipients’ inboxes. Remember, your email marketing strategy is only as good as how many inboxes it makes it into.

Email list cleaning is as crucial as growing a healthy list. Cleaning your email list ensures your email campaign reaches only engaged customers interested in your brand. Also, don’t neglect to maintain a healthy email list for long-term growth.

Do you think it’s time to clean your email list? Try out Klaviyo to automate your email list cleaning process.

Do you think it’s time to clean your list?
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Maddy Osman
Maddy Osman
Maddy Osman is the author of Writing for Humans and Robots: The New Rules of Content Style. She's a digital native with a decade-long devotion to creating engaging, accessible, and relevant content. Her efforts have earned her a spot in BuzzSumo’s Top 100 Content Marketers and The Write Life’s 100 Best Websites for Writers. She has spoken for audiences at WordCamp US, SearchCon, and Denver Startup Week.