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Soft Bounce Vs Hard Bounce: What's The Difference?

Understanding the difference between the terms soft bounce" and "hard bounce" is important for anyone aiming to run a successful campaign. Both terms relate to issues that can occur when sending emails, and each can significantly impact your hard bounce rate. Identifying and addressing these issues is important to maintaining a healthy email list and fostering strong relationships with your recipients.

In this article, we will explain the key differences between soft and hard bounce. We will also explore the various causes of these bounces and offer insights into how you can improve email deliverability and email bounce rate and ensure your email messages reach their intended recipients.

What Is a Soft Bounce?

In email marketing, a soft bounce is a temporary failure in email delivery. The email gets as far as the recipient's mail server, indicating that the email address is valid. However, the email message bounced back before reaching the customer's inbox. Several factors contribute to soft bounces, affecting your overall effort to improve email deliverability rates.

Soft bounces can happen due to the following reasons:

Understanding these factors is crucial for addressing issues related to what is a soft bounce and for lowering your hard bounce rate.

What Is a Hard Bounce?

Unlike a soft bounce, a hard bounce is a permanent failure in email delivery. This typically happens when the customer's email address is either invalid or no longer in use. Such failures are detrimental to your email campaigns and can inflate your hard bounce rate if not addressed promptly.

Hard bounces can occur due to the following reasons:

Hard bounces are particularly challenging because Internet Service Providers (ISPs) will send back response codes indicating why your email failed to deliver. These response codes can vary between different ISPs and mail servers, adding another layer of complexity to understanding what is a hard bounce.

Hard bounces are permanent delivery failures, usually due to an invalid email address or non-existent email address. They need immediate attention, as they can significantly impact your hard bounce rate and overall email deliverability.

Different Causes of Soft Bounces and How to Fix Them

Below are some common reasons for soft bounces and suggested solutions for each issue:

1. Mailbox Full

A full mailbox can sometimes cause soft bounces. If you've been sending emails to a customer that were previously delivered but are now failing, the email is temporarily categorized as a soft bounce by the ISP. After 2-3 days, if delivery continues to fail, it may be classified as a hard bounce.

How to Fix:

2. DNS Failure

DNS failure happens when an email can't be delivered due to DNS issues at the recipient's end. The issue could be a down server, a typo in the setup, or a non-existent domain.

How to Fix:

3. Challenge-Response Error

Some email filtering services send a challenge-response reply to filter emails from unknown senders. If the challenge isn't completed correctly, the email isn't delivered.

How to Fix:

4. Vacation/Out of Office/Auto-Reply Emails

Auto-reply emails usually indicate the customer is temporarily unavailable, meaning the email will likely be read at a later time

How to Fix:

5. Other Errors

Sometimes, the reason for a soft bounce can't be determined, usually due to a technical issue like a timed-out connection.

How to Fix:

Different Causes of Hard Bounces and How to Fix Them

Understanding hard bounces is just as critical as understanding soft bounces when it comes to maintaining a healthy email list and boosting the effectiveness of your email marketing campaigns. Here, we will explain the different categories of hard bounces and provide ways to fix each specific cause.

1. Recipient Does Not Exist

When the Internet Service Provider (ISP) reports that an email address doesn't exist, this is akin to a post office declaring that there's no such person at a given address. Persistently sending emails to non-existent addresses can tarnish your sending reputation, affecting your business and your email service provider, like Constant Contact.

How to Fix:

2. Mailbox Full

This differs from the soft bounce category for a "Mailbox Full." The full mailbox is a consistent issue, indicating that the email address may have been abandoned. This is commonly seen in special-purpose email accounts that people no longer use.

How to Fix:

3. Blocked Email Address

ISPs may block email addresses due to suspicions of spam or other security policies. This is especially crucial when it comes to your sender reputation and can involve aspects like DMARC, DKIM, and SPF authentication failures.

How to Fix:

4. Rejected by Spam Filters

Sometimes, an email or its subject line contains content that triggers the spam filters of the ISP. If a customer has previously marked your emails as spam, all future emails will likely end up in their spam folder.

How to Fix:


In this article, we've explained the different causes of hard and soft bounces in email marketing and how to address them. These issues, if not handled correctly, can impact your email deliverability and, subsequently, the success of your email campaigns. Implementing the solutions we've discussed can go a long way in ensuring your emails reach the intended inboxes.

For a comprehensive solution to all your email marketing needs, including robust features that help you manage bounces effectively, check out our platform, SendNow.

Visit SendNow to explore the wide range of features and services they offer to enhance your email marketing strategies.

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