Email Bounce Codes Errors (List + Troubleshooting)

Delivering an email is simple until it isn't (especially when you’re sending mass emails).

Email bounce rates not only interrupt your well-crafted email campaigns but also tarnish your sender's reputation. Radicati says, by the year 2025, more than 375 billion emails are expected to be sent and received every day. If just 1% of these encounters a bounce error, we're looking at over 3 billion mysteries a day!

Understanding email bounce code errors is the first step toward tackling the problem. The conundrum lies in the fact that these codes are fundamentally impersonal. They are engineered for mail servers, not for email marketers struggling to comprehend them. This makes it even more important for email marketers to get it right.
So, let's get cracking!

Email bounce codes are automated responses from a recipient's mail server, providing reasons for the non-delivery of an email you sent. Each email bounce comes with such a cryptic code that marketers need to troubleshoot to ensure smooth future deliveries.

SMTP (Simple Mail Transfer Protocol) defines this code, and it's your only clue as to why your message was rejected. Sometimes, these codes are paired with error messages, often unique to each mail server and mystifying in their own right.

To ensure that your campaigns reach their intended audience with minimal disruption, it is crucial to understand the nature of these codes.

Email bounce codes can be broadly classified into two categories: Soft Bounce Codes and Hard Bounce Codes.

Understanding these categories is key to fine-tuning your email marketing strategies. Here’s a quick explainer on both:

In such a scenario, it's best to avoid sending emails to the hard-bounced ones, while soft-bounced ones can be contacted again.

Most marketers also prefer minimizing the risk of bounces even before sending out the campaigns by verifying emails and removing the invalid/non-existent ones.

According to a study by ReturnPath, an average of 20% of all emails never reach the inbox—that’s 1 out of 5 emails! This makes understanding the reasons behind email bounce codes a critical skill for every email marketer.

Let’s look at six common causes behind these unwelcome bounces:

Traditional SMTP bounce codes are three-digit numbers indicating whether the delivery succeeded or failed. Enhanced SMTP bounce codes, however, are more detailed, giving a deeper insight into delivery failures.

Now, let's explore these codes in detail:

In the three-number SMTP bounce codes, the first digit represents the delivery class:

• 2.X.X signifies successful delivery


• 4.X.X denotes issues in delivery temporarily


• 5.X.X refers to permanent issues

The second digit pinpoints where things go wrong. For example:

• In X.1.X, the '1' indicates an addressing issue


• X.2.X represents an issue with the mailbox


• X.3.X denotes a mail system issue

The third digit provides further detail on the specific issue. For example, 4.1.1 means there’s a temporary failure, or the host isn’t answering.

Here’s a comprehensive email bounce code list for enhanced SMTP bounce codes:

Here’s a comprehensive email bounce code list for traditional SMTP bounce codes:

It is next to impossible to memorize the entire server lingo and remember every code and its description. However, learning the basics of email bounce code interpretation can be done easily.

When you're running campaigns with mass emailing, navigating through email bounce codes becomes a complex never-ending task. You need to ensure that you're well-equipped with the right tools and strategies.

Let's explore four actionable tips needed to handle and mitigate the impact of these bounce codes. Here are some tips for the same:

Label your subscribers based on their acquisition source. This way, you can identify which source is causing a significant number of bouncebacks. If a particular source leads to higher bounce rates, it might be beneficial to stop using it.

This strategy is suggested by Chad White, an Email Marketing Expert and Head of Research for Oracle Marketing Cloud Consulting. Adding to the details, he says:

If you plan to purchase an email list, be prepared for a high bounce rate. Additionally, inappropriate email mining tools and human errors, like mistyping an address, also contribute to bounces.

The more effort you put into validating and cleaning your email lists, the lesser the email bounces rates.

If you're consistently getting email bounce codes suggesting that your emails are being blocked or treated as spam, it may be a sign that your sender's reputation is poor.

Use tools to monitor your sender score and take steps to improve it, such as warming up your IP address, following email marketing best practices, and ensuring high engagement rates.

Maintain a regular email-sending schedule. If you send emails infrequently, you run the risk of email addresses on your list becoming invalid between sends.

Besides that, make sure you’re aware of your sending limits. Especially if you're using email service providers., exceeding your daily limits will result in your emails bouncing. You can also implement a system that either slows down your sending rate as you approach the limit or pauses the campaign once the limit is reached.

Managing email bounce error codes effectively is crucial to achieving a higher deliverability rate. Understanding the codes, distinguishing between traditional and enhanced SMTP bounces, and knowing how to troubleshoot common issues can significantly improve your email marketing results.

Clearout stands as a pivotal tool for email marketers, ensuring real-time email verification and comprehensive list cleaning. Its robust technology dramatically cuts down both hard and soft bounces.

The Guaranteed Deliverables feature also ensures you are landing into your recipient’s inbox without major bounces (less than 3%). Thus, with email verification before launching email campaigns, and proactive cleaning, Clearout enhances your deliverability, amplifies your campaign effectiveness, driving better engagement and higher ROI.