Hard Bounce, Soft Bounce in Email Marketing & How To Improve Bounce Rate

We understand the deep frustration that arises when you invest time and effort in crafting emails, only to discover that some of them never reached their intended recipients. At this point, you might consider starting fresh and writing new emails, but doing so ignores the root issue.

The occurrence of email bounce indicates potential problems with your email deliverability. If your email bounce rate is high, it raises the likelihood of your domain getting blacklisted by various Internet Service Providers (ISPs). Needless to say, this is far from an ideal situation.

Therefore, it’s crucial to grasp the significance of your email bounce rate and take measures to understand the different types of bounces that may occur. In this blog, we will delve into the concepts of email hard and soft bounces, highlighting their main distinctions, and providing guidance on how to effectively manage them.

What is a Bounced Email?

A bounced email refers to a message that is returned to the sender because it could not be delivered to the intended recipient. Several factors can lead to email bounces, such as an invalid email address, a full mailbox, or a server error. When an email bounces, an automatic response is generated, notifying the sender of the failed delivery.

There are several reasons why emails may bounce. One common cause is when a subscriber provides an incorrect email address. Bounces can also happen due to temporary server outages or when the recipient’s inbox has reached its storage limit.

When your emails bounce frequently, it may indicate potential issues on your end. For instance, it could be a result of your emails being flagged as spam multiple times, or it might be due to having a restrictive DMARC (Domain-based Message Authentication, Reporting, and Conformance) policy in place. Keeping a close eye on your bounce rates can help you identify and address these problems, ensuring better email deliverability and communication with your recipients.

A Bounced Email Notification

A bounced email notification serves to inform the sender that an email they attempted to deliver was unsuccessful. The typical content of a bounced email notification includes:

  1. Date and time of the bounced email: This indicates when the email delivery was attempted and subsequently bounced back.
  2. The mail server that bounced it: The notification specifies the mail server that encountered the delivery issue and rejected the email.
  3. The RFC code and the reason for the bounce: The RFC (Request for Comments) code is a standardized code that classifies the type of bounce. An email hard bounce is represented by a 5XX code, while an email soft bounce is depicted by a 4XX code. The code is accompanied by a specific reason for the bounce, such as “mailbox full,” “invalid recipient address,” or “server error.”

However, it’s worth noting that not all Internet Service Providers (ISPs) strictly adhere to these RFC codes for bounces. Some ISPs may use their custom codes or provide more general explanations for the bounce reasons. As a result, interpreting bounce codes accurately can sometimes be challenging, but understanding the common reasons for bounces remains essential for email deliverability management.

The Difference Between Hard Bounce & Soft Bounce

Two categories of email bounce exist hard bounce and soft bounce. These two types of email bounce exhibit notable distinctions. Here are some of the differences between them:

Hard bounce

  1. The recipient doesn’t exist

If an email address is non-existent, the email can bounce. In such cases, Mailmunch designates these bounced emails as “Failed” and ceases sending further emails to that recipient.

This precaution is taken to safeguard the sender’s reputation of both your business and Mailmunch. Repeatedly sending emails to non-existent addresses can have negative consequences on email deliverability and sender credibility.

To address this problem, you should verify the email address for any obvious typos. Additionally, consider reaching out to your customer through an alternative channel to inquire if they have a new email address.

If the problem persists, you can seek assistance from our support team to resolve the issue.

  1. Blocked email addresses

Frequently, emails experience hard bounces when the Internet Service Provider (ISP) blocks the sender’s email address. This blocking occurs because the ISP identifies the emails coming from this address as potential spam.

Moreover, ISPs implement specific email security measures like DMARC, DKIM, and SPF. For your emails to reach the intended recipient, they must successfully pass through these security layers. If any of these security checks fail, the email will not be delivered.

In the case of a blocked bounce from a smaller domain, resolving the issue can be achieved by reaching out to the ISP directly.

  1. Spam filters

Occasionally, ISP spam filters identify certain content in your emails as suspicious, leading them to be flagged as spam. Additionally, if a customer signs up for your email list but marks one of your emails as spam, subsequent emails may be automatically diverted to their spam folder.

If you observe a customer consistently listed as “did not open” in your reports, it is essential to reevaluate your approach and craft engaging content to pique their interest. If the customer remains unengaged despite efforts to re-engage them, it is advisable to remove them from your email list.

Soft Bounce

Email soft bounces, while less severe than hard bounces, represent temporary failures in email delivery. Soft bounces can happen for reasons such as:

  1. A full mailbox
  2. DNS failure
  3. Challenge-response error
  4. Malicious and spammy content

A full mailbox

When recipients fail to clear their inboxes, some emails bounce due to mailbox full issues. Initially, if your recipient has received emails from you in the past but now experiences bounces, these will be classified as soft bounces.

The ISP monitors the frequency of delivery failures over a period of two to three days and attempts to deliver the email during this time. If, after this period, the emails remain undelivered, they are then categorized as hard bounces.

To address this, it is recommended to contact your customers and notify them about their full mailbox. Additionally, inquire if they have a new email address. If the issue persists, consider removing these customers from your email list.

Furthermore, if a customer reports not receiving your emails, advise them to check their spam folder. If the email is not in the spam folder, suggest they add your email address to their email account’s safelist or security program.

DNS Failure

The Domain Name System (DNS) failure occurs when your recipient’s email server faces issues in delivering your email. This problem can either be temporary or persistent. It may be caused by the email server being down or overwhelmed due to a large influx of incoming emails.

If you encounter a DNS failure, it’s advisable to attempt sending the emails again after a day or two. If the problem is temporary, it is likely to be resolved during that time.

Challenge-response error

The customer sets up a challenge-response system to screen emails from unfamiliar senders and spam messages.

This system generates an automated “challenge,” often in the form of a question or action, which the sender must correctly respond to within a specified timeframe for the email to be delivered.

To address this challenge-response mechanism, you can implement permission-based email marketing by utilizing double-opt-ins. This means customers must respond to an email confirmation to be added to your email list.

Additionally, it is advisable to conduct spam tests on all your emails before sending them. This process helps identify words and phrases that may trigger spam filters. More information on this topic can be found below.

Auto-reply emails

Automated response emails signify that your customer is currently unavailable. These notifications serve as valuable indicators, especially when sending time-sensitive information, as they inform you that your customer will not access the email promptly.

Furthermore, you have the option to send your email to a contact using a role address that belongs to another person but has auto-reply functionality activated.

How to improve your email bounce rate?

  1. Use double opt-ins

Utilizing double opt-ins is a beneficial approach to minimize email bounce rates. With this method, once customers join your email list, they need to confirm their sign-up by clicking a verification link sent to their inbox. This process ensures that the email addresses collected are valid and capable of receiving your emails.

  1. Maintain list hygiene

Ensuring list cleanliness is vital for enhancing your email bounce rate. Consistently purging your email list and eliminating invalid or inactive email addresses guarantees that your messages reach only active and engaged subscribers who have a genuine interest in your content.

Furthermore, in addition to monitoring the bounce rate, it is essential to pay attention to other email marketing metrics like open rates and click-through rates to identify inactive subscribers. This approach helps maintain a responsive and interested email audience.

  1. Send emails consistently

Consistently sending emails will reduce your email bounce rate. Regular engagement with your subscribers increases the chances of them remembering and interacting with your emails. Conversely, if new subscribers don’t receive emails from you for extended periods, they are more likely to forget about you and may even mark your emails as spam.

  1. Verify your domain

As per Litmus, only 40% of companies successfully complete the domain authentication process, which can negatively impact their email deliverability rate. Domain authentication can be achieved through DMARC, SPF, and DKIM methods.

Having an authenticated domain leads to improvements in email hard bounce and soft bounce rates. Additionally, it boosts deliverability rates and ensures that subscribers do not receive security alerts when opening your emails.

  1. Don’t use spammy language in your emails

You may inadvertently use spam-related words in your emails, so it’s crucial to avoid such language to enhance your email’s hard bounce rates. Spam filters are designed to detect and block emails that contain certain words, phrases, and images commonly associated with spam. To improve deliverability rates, refrain from using words like:


“X% Off”

“Make Money”

“Free Offer”

In addition, it’s advisable to avoid excessive use of emojis in your subject lines, as this may lead to your emails being marked as spam and impact deliverability rates. Furthermore, be cautious about using too many dollar signs in your emails to maintain a positive sender reputation.

  1. Segment your list

By utilizing a segmented email list, you can guarantee that only highly engaged customers receive your emails. This approach enables you to understand your customers better and send them personalized content based on their interactions with your emails.

Segmenting your email list according to factors such as location, gender, and preferences allows you to tailor your email content to the specific interests of each group, ensuring that they find the emails more relevant and engaging.

  1. Monitor your email deliverability

It is essential to consistently monitor your email deliverability and not rely solely on past strategies. Customer interests can change rapidly, and their disengagement or marking emails as spam can impact your email deliverability negatively.

To understand what content resonates with your customers, conduct A/B tests on your emails regularly. Additionally, closely track your email bounce rates and deliverability rates to detect any issues before they escalate into significant problems. This proactive approach ensures that you maintain a strong email performance and customer engagement.

  1. Use a preference center

Implementing a preference center can enhance your subscriber management efficiency. Through this center, you empower your customers to control the types of emails they wish to receive, thereby obtaining precise information about their preferences.

A standard preference center enables customers to update their email addresses, select their preferred email frequency, and opt out of your email list. Additionally, you have the option to include features like sharing information about user preferences. Placing the preference center link in the email footer allows easy access for your customers to make their desired selections.


Unaddressed email hard bounce and soft bounce issues can lead to significant challenges. Ignoring your email bounce rate can harm your sender’s reputation and negatively impact email deliverability.

However, you can resolve this problem by adopting various measures, including keeping a clean email list, maintaining regular and consistent email-sending practices, verifying your domain, and leveraging an email marketing platform. These steps will help ensure the successful deliverability of your emails and mitigate bounce-related complications.