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Silvestras · 11 min read · Tips and resources · September 28, 2020

Your guide to understanding soft and hard email bounces

Have you experienced this email marketing conundrum? You upload your subscriber list, send off the email campaign, and… your subscriber number drops.

Where did they all go? Seasoned email marketers will go straight to their campaign report to find out whether their audience has been hitting ‘Unsubscribe’. If they’ve stayed on top of their email list management, this is usually the only reason why subscribers are disappearing mysteriously. 

However, if you are not staying on top of your subscriber metrics, there is another reason you might be losing people—soft and hard bounces. In this blog article, we’re going to walk you through: 

  • What bounced emails are.

  • The difference between soft and hard email bounces.

  • Common reasons for bounced emails.

  • How to stop your email campaign from bouncing.

Let’s hop to it and jump in (bounce puns intended)!

Now, the word ‘bounce’ might sound like fun, but the reality is a bit more annoying. In simple terms:

A bounced email is an email that couldn't be delivered to the recipient.

Your subscriber’s server will bounce the email back for a variety of reasons, which we will explain in the next section. If you want to see if emails are bouncing, you can find out in your email campaign report. 

Bounces can seriously impact your email delivery rates. If your email isn’t getting into your subscribers’ inbox, you could end up with a number of issues including poor delivery rates. 

But don’t worry. We’re going to talk you through the different types of email bounces, and then explain how you can tackle them. 

When we talk about email bounces, there are two main types that you’ll hear about: soft bounces and hard bounces. 

A soft bounce is a temporary issue, where the email reaches the recipient’s email server but bounces back undelivered. Soft bounces could be caused by several reasons, such as a full mailbox, an offline email server, or a message file that’s too large.

A hard bounce is an email that couldn’t be delivered for permanent reasons, such as the address doesn't exist or the server has blocked you. The email is returned to the sender and is completely undeliverable. When this occurs, your email marketing tool will no longer send emails to those email addresses. A high volume of hard bounces is problematic for email deliverability.

When emails bounce, it usually has nothing to do with your email marketing software. Your email tool will successfully send out the email, but then the subscriber’s email server rejects it for some reason. What are those reasons? We’re glad you asked.

Reasons for soft bounces: 

  • Mailbox full: Some of your subscribers’ mailboxes have limitations in terms of capacity. If this limit is reached, your email campaign will be bounced back to you. 

  • Server timeout: The subscriber’s email server may be temporarily unavailable, overloaded, or undergoing maintenance, and any incoming messages will bounce. If this happens, you can try resending your campaign the next day.

  • Oversized message: This is rare, but some inboxes have sensitive filters that restrict the message size. Make sure your email isn’t overloaded with GIFs and images, or it might bounce.

  • Email account temporarily suspended: If the subscriber has not signed in for more than 365 days, or if their server has detected suspicious activity, their account could be locked temporarily. Which means… (yep, you got it)... the email will bounce.

  • DMARC requirements: Your email message might not meet the recipient server’s DMARC requirements for authentication. Simply put, the server can't verify the sender.

Reasons for hard bounces:

  • Email address does not exist: Invalid emails are the most common reason for hard bounces. This happens when the recipient’s address has a typo in it, or they have disabled the address and/or switched providers. 

  • Email message blocked by the recipient’s server: Some corporate, government and institutional domains have stricter inbox filter settings. 

hard vs soft bounce comparison red purple signs - MailerLite

To put it plainly, both soft and hard bounce rates spell trouble. Here, we’ve put together a list of our top 4 best practices to help you improve your email bounce rate. 

1. Use double opt-in

When collecting your subscribers, always use double opt-in forms. This is where, after signing up, the subscriber will receive a confirmation email, where they must click a link to verify their email address. This extra step reduces the chances of spam email addresses ending up on your subscriber list.

👉 Tip

Only use subscriber list-building strategies that you trust and are reliable. Purchasing email addresses is a huge mistake, and it will come back to bite you!

 2. Maintain your email list hygiene

The key to avoiding bounces is to maintain a high-quality email list. Use email validation tools like Mailercheck to verify and clean your subscriber lists. When it comes to email address verification, look for tools that go beyond list validation, and provide valuable email list analysis. These insights can help you manage your list and find emails that can potentially be saved. 

Sometimes, a subscriber may not have given you a valid email address. Always double-check for typos in your subscriber lists, to avoid any hard bounces. 

If you transfer to another email marketing tool, make sure you only upload your active subscribers. An accumulation of invalid email addresses could severely impact your email deliverability. 

Last but not least, you can also ask your subscribers directly for updated information. Try linking your subscribers to a landing page in your next newsletter. Ask them if they would like to update their details or content preferences. 

3. Authenticate your domain

Authenticating your domain is like going through passport control before you enter a new country: the border police will want to check your credentials, before letting you through. In email marketing, an authenticated domain will legitimize your account, as Internet service providers (ISPs) like Gmail and Outlook can better route the origin of your email. 

In addition to authenticating your domain, it's a good practice to ask your subscribers to add your email address to their inbox address book. 

You can authenticate your domain directly on your dashboard if you use MailerLite. Check out our handy guide on how to authenticate my domain

👉 Tip

We recommend that you do not use free sender domains, such as ‘’. Free email domains cannot be authenticated.

4. Keep your timing consistent during email campaigns

Consistency is key. Set up an email cadence strategy so your subscribers anticipate regular and consistent contact from you. An email cadence is a combination of the number of emails you send during a certain period of time (frequency), the type of emails and the best times to send your emails.

When there is constant communication between you and your subscribers, the email service recognizes the activity as normal. In email marketing, 'normal' is a good thing.

Campaign reports dashboard bounced emails - MailerLite

You can access your bounce stats in your MailerLite campaign reports. When you open up a campaign report, you will see 2 bounce sections: soft bounce and hard bounce.

With MailerLite, a soft bounced email address will remain active on your subscriber list. However, after soft bouncing for 3 consecutive times, it will be converted to hard bounce and become inactive. 

MailerLite automatically moves subscribers that hard bounce into a ‘Bounced subscribers’ category, so that they don’t receive future campaigns. This means that you don’t have to remove subscribers sitting in the ‘Bounced’ tab - we do it for you. If you think that there’s been a mistake with a particular hard bounced email, reach out and contact us and we’ll check our bounce log.

According to our Anti-Spam policy, we have the right to suspend your account if the bounce rate is above 5%. You will be warned and asked to clean your list with an online email validation tool. This is done to ensure the quality of our servers and your sender reputation.

If you’d like to learn more, you can check out our email campaign reports feature, or watch our email campaign reports tutorial

Your subscriber list is the engine of your entire email marketing operation. In the same way a car must be maintained to work properly, the health of your email marketing relies on keeping your list in great condition.  

Subscriber lists with fewer bounces will give you better deliverability, higher open rates and a sender reputation that will put a smile on your face. To make your list the best it can be, remember to:

  • Keep your subscriber list clean, by using an email validation tool such as Mailercheck

  • Use double opt-in to ensure you are adding valid subscribers.

  • Authenticate your email domain and maintain a healthy sender reputation. 

  • Send consistent email campaigns to improve opens, and avoid any ‘spammy’ content!

  • Keep track of your bounce rates with the email campaign reports on your MailerLite dashboard.

You’re on your way to a bounce-free universe! 

Editor's note: This post was originally published in October 2017, but it has been updated with new guidance on understanding soft and hard email bounces. 

Silvestras Armonaitis

Hi, it’s Silvestras, a member of MailerLite’s customer support team. As the first remote employee to join MailerLite in 2014, I was the guinea pig to test if remote work was a good idea. Today, MailerLite is a remote-first company so the experiment was a success! To all the other remote workers who have joined since—you’re welcome.