Silvestras from MailerLite

Silvestras5 min readTips and resourcesOctober 25, 2017

Understanding soft and hard email bounces

Understanding soft and hard email bounces

We sometimes get this question: “I have uploaded my list, sent a campaign and now I see my subscriber number has dropped. Where did they all go?”

While this may seem puzzling at first, seasoned email marketers will jump straight into the campaign report to see what happened there. If you have been taking good care of your list, the only reason why the subscriber number might drop must be the Unsubscribed tab.

However, there is also this mysterious Bounced tab. What is it doing and why do some subscribers ended up there you might wonder.

In this blog post, we will guide you through the world of bounces and how to deal with them.

The meaning of bounced email

In short, bounced emails are addresses that could not be delivered successfully to recipients of email marketing campaigns. For various reasons, the recipient’s server will return the newsletter to the sender, hence the term “bounce“.

When asked to explain bounces, I remembered a funny video: “Why does the ball bounce?” – a famous comedian once asked Kobe Bryant. While Kobe’s reply explains the reason (air) for a specific object (basketball), the same reason does not apply for a different object (room).

The same goes with bounces – some emails are affected by them, while others are immune. Let’s find out why!

What is a soft and hard bounce in email marketing?

All bounces can be divided into two main categories. When you open up a campaign report, you will notice 2 bounced tabs – soft bounce and hard bounce.

A soft bounce is an email message that gets as far as the recipient’s mail server (it recognizes the existing address) but is bounced back undelivered before it gets to the intended recipient. It is a temporary issue.

A hard bounce is an email message that has been returned to the sender and is permanently undeliverable.

Soft bounce reasons

Here are the possible reasons for soft bounces and how to deal with them:

  • Full mailbox. Some of your recipients’ mailboxes have limitations in terms of capacity. If this limit is reached, your newsletter will be bounced back. The subscriber will remain active in your MailerLite account and you can try resending the campaign to this subscriber the next day.
  • Server timeout. As servers are not 100% issue-proof, sometimes the message will not be delivered. It can happen due to recipient’s server being overloaded, temporarily unavailable or under maintenance. In such case, we recommend resending the campaign to such recipient at a later time.
  • Message too large. Although this normally never happens, some recipients’ inboxes might have sensitive filters, that restrict the message size. Check your campaign, make sure it’s not a kilometer long heavily loaded with huge images and .gif files.

An important thing to note is that in MailerLite a soft bounced email address will remain active. However, after soft bouncing for 5 consecutive times it will become hard bounce and inactive.

Hard bounce reasons

Here are the popular hard bounce reasons:

  • Email address does not exist. This is the most common hard bounce reason. Normally this happens if the email address has a typo in it or the owner has disabled the address or maybe switched providers. If you notice a lot of hard bounces in your first campaign to a new list – you will have to verify the rest of the list with an online email validation tool, such as NeverBounce.
  • Email blocked by recipient’s server. Some corporate, government, institutional domains have stricter spam filter settings. While sometimes your sender domain authentication can solve the issue if you are still being blocked – contact the recipient and ask to add your sender email address to their inbox address book.

Tips and general advice

Bounces, especially hard ones, are actually damaging your sender reputation. If your bounce rate is high (above 5%), it means that you also have a lot of non-existing email addresses in your database.

By sending to a non-existing email address you can hit a spamtrap. This would result in a significant damage in terms of deliverability. Your campaigns would land into a spam folder and some stricter spam filters might block them altogether.

The good news is that MailerLite automatically moves subscribers that hard bounce into a “Bounced Subscribers” category, so they don’t receive future campaigns. This means that you don’t need to remove subscribers sitting in “Bounced” tab – we do it for you.

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.


  • always make sure you are uploading only active subscribers when moving from another ESP.
  • always use double opt-in to collect email addresses. It will discard fake email addresses (sometimes recipients enter fake email addresses in order to just receive freebies) via confirmation link that is sent to the recipient during the opt-in and it may resolve a lot of issues.
  • if you haven’t sent a single campaign to a list for more than a year – it’s a good idea to validate that list.
  • use a trustworthy email validation tool, such as NeverBounce. Cheap or free tools are not reliable.
  • if you think there’s a mistake with a particular hard bounced email – contact us and we’ll check the bounce log.
  • use reliable opt-in tools to collect subscribers. Don’t use purchased, rented, publicly available or 3rd party lists.

Bounce-free lists lead to better deliverability, higher open rates, and bigger profits. Use these tips and knowledge to your advantage.

Good luck and happy mailing!

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.