Bounce back emails make unpleasant reading for any marketer. You can spend hours crafting the perfect outreach email, only for the message never to reach the intended recipient.
What’s more, these notifications signify a problem with your email list. If one email address is wrong or out of service, how many more could be inaccurate?
To get to the root of the problem, it’s important to understand why you’re receiving bounce back emails, and what you can do about it. In this guide, we’re going to explore both topics in depth.
What Exactly Is a Bounce Back Email?
A bounce back email, also known as a Non-Delivery Report (NDR) or a Delivery Status Notification (DSN), is essentially an error message. It tells you that an email you just sent did not reach a working inbox, and provides a few details about the problem:
- The issue that has caused the bounce
- A unique email ID
- The time when the bounce ocurred
- The hostname and IP address of the recipient server
- An error message or SMTP error code
With individual messages, an occasional bounce is nothing more than an inconvenience. When you’re sending thousands of messages in an email campaign, a high bounce rate can be a major problem.
Emails may bounce for a variety of reasons:
- The Incorrect Email Address: If you misspell a recipient address or send to a non-existent email address, the message will bounce.
- Mail Server and Domain Problems: A misconfigured email server or email domain can cause messages to be rejected.
- Capacity and Policy Limits: A full mailbox will return to the sender. In addition, some email accounts are set up to reject certain types of incoming email (e.g. messages that break file size limits).
- Security Filters: Email accounts will sometimes reject messages that look like spam or some kind of cybersecurity threat.
We will take a closer look at each of these issues later, along with some key troubleshooting steps.
4 Common Types of Email Bounces
Not every bounce back email is exactly the same. In fact, there are four different categories of bounced messages and associated error codes. Some indicate a temporary issue, while others tell us there is a permanent failure.
Soft Bounce (4.X.X Error Codes)
A soft bounce is caused by a temporary delivery issue, such as email server downtime or an inbox that has reached maximum capacity.
When your email client receives a soft bounce notification, it will probably try to send your email again several times within the next 72 hours, in the hope that the problem will clear.
Hard Bounce (5.X.X Error Codes)
At the opposite end of the scale, we have a hard bounce. This type of bounce back message denotes an issue that isn’t likely to be resolved any time soon. For instance, resending an email to an address that doesn’t exist is a losing game.
Transient Bounce (Usually 4.X.X Codes)
A transient bounce is a variant of the soft bounce, where the problem might only last minutes. Classic examples include server downtime for maintenance, network issues, or a server that is overloaded with requests. As with a soft bounce, your email provider will respond to such notifications by trying again.
Unspecified Bounce
There are occasions when the reason for a bounce isn’t clear. This can happen when a server provides an ambiguous error message, or doesn’t respond at all. Unspecified bounces can be tricky to deal with, because it’s almost impossible to diagnose the underlying problem.
What Is an Acceptable Email Bounce Rate?
When you’re sending email messages at scale, some bounce back is inevitable. Most marketers consider 2% as a benchmark. However, it’s worth remembering that bounce rates are like limbo dancing. The best go low.
While the exact figure varies across industries, a study of one million marketing campaigns from verified accounts found that the average email bounce rate was 0.3%. Other research suggests that this average figure tends to rise as emails become more infrequent.
A bounce rate below 1% might not be realistic for every business. But it’s certainly a worthy goal.
How to Find Your Email Bounce Rate
Measuring your current bounce rate, and tracking this metric over time, is important if you want to improve email deliverability and open rates.
To calculate your current bounce rate, use this formula:
Bounce Rate = (Bounced Emails / Total Sent Emails) × 100
Why Should I Care About Bounce Back Emails?
Some marketers pay little attention to bounce rate. They just see a temporary halt in communication — nothing to worry about.
The reality is quite different. For a start, every bounced email message is a missed opportunity to make a sale or start a conversation. If you can prevent such mishaps, the long-term benefit is reduced customer acquisition costs and better customer lifetime revenue.
Perhaps more importantly, a high bounce rate can damage your sender reputation. This is a metric that email service providers use to track accounts that send spam emails.
If the IP address of your email server becomes associated with poor deliverability, you may find that future messages are categorized as junk, even when they are completely legitimate.
Other disadvantages of a high bounce rate include:
- Wasted resources: Every bounce counts towards the monthly allowance of your email service provider (ESP). Plus, incorrect email addresses take up space in your database.
- Skewed Data: When you’re trying to measure the performance of individual campaigns, a high bounce rate can make it difficult to draw firm conclusions.
- Blacklisting (or blocklisting): Companies that have a persistently high bounce rate can even be blocked by ISPs.
Just to add to this lengthy list of reasons to care, a high incidence of bounce back emails can hint at serious compliance issues, such as not adhering to GDPR best practices.
Why Your Emails Bounce Back
To avoid these problems and improve your overall deliverability, you first need to figure out why your emails are bouncing.
As we mentioned earlier, there are many types of email bounce and multiple potential causes. Here’s a closer look at the most common reasons:
Spam Filters
In an attempt to protect users, email platforms use spam filters to detect unwanted emails. These filters take into account many different attributes, but salesy language is often a key trigger.
Messages that are stuffed with terms like free, buy now, and guaranteed are sometimes blocked, leading to a bounce back.
Full Mailbox
Most email service providers place limits on inbox storage. When an account reaches this limit, it may stop accepting new mail altogether, leading to a bounce. This happens surprisingly frequently, particularly with accounts that don’t see much active use.
Invalid Email Address
It only takes one wrong character to invalidate an entire email address. Unsurprisingly, this is a very common cause of bounce back — especially when users have to enter their email address manually. Poor data handling practices can also corrupt email addresses.
Technical Issues
A range of technical issues can cause a bounce. Mail server issues, misconfigured DNS records, or problems with custom email servers are all in the mix. Even connection problems and issues with the recipient’s ISP can take a toll on deliverability.
Email Is Too Large
Just as most mailbox providers put a cap on storage, many will only accept messages and file attachments up to a certain size. If your email exceeds these quotas, you may get a bounce back. As one example, Gmail will only accept attachments up to 25 MB.
You've Been Blocked
It’s not only spam filters that might weed out your messages. If your IP address is blacklisted, or someone has blocked your email address manually, you can expect future emails to bounce. This occurs when brands send too many messages; both users and email platforms take action to stop the unwanted noise.
Your Sender Reputation Score Is Low
If you rack up too many bounce rate problems or spam complaints, your IP address may lose credibility and your sender reputation score will drop. In turn, you’re likely to encounter more problems with filters and other protection. This downward spiral is certainly worth avoiding.
7 Essential Steps to Prevent Bounce Back Emails
Understanding the cause of your delivery failure is one thing — but how do you actually cure a rising bounce rate? It turns out, there are several steps you can take to solve the problem.
Clean Email Lists Regularly
Even if you only have a few dozen subscribers, there is a high chance that your email list contains some dead email addresses. There might be a few misspelled ones, too.
At a small scale, you could just find and correct these errant records manually. But once your list reaches the thousands, the problem can quickly get out of hand.
A better way to approach this task is by utilizing a dedicated cleaning tool, like NeverBounce. Instead of combing through your records by hand, you simply upload the entire list and let the platform find bad records. It takes just seconds, and NeverBounce detects 99.9% of incorrect and inactive email addresses.
Of course, lists don’t remain the same for long. Email marketers spend much of their time trying to attract as many new subscribers as possible. To help you stay on top of email list cleaning, NeverBounce connects your email solution or CRM and automatically imports new records every day. The platform then cleans away the junk, leaving you with verified addresses.
Verify Email Addresses When They're Collected
List cleaning is vital for keeping existing records up to date. But did you know that you can verify email addresses before they are added to your list? Whether it’s a lead generation form or a simple newsletter signup, this type of proactive maintenance can reduce your bounce rate over time.
NeverBounce has this option built in. Our Verify feature allows you to add real-time email verification to your forms and apps via a custom API, a JavaScript widget, or even through Zapier.
Using a solution like this ensures that bad emails don’t get into your database in the first place.
Keep Up Your Sender Reputation
Sender reputation works a bit like a credit score. Keep it healthy, and you will have the leeway to build massive email marketing campaigns. Allow your score to fall, and it will require plenty of work to put it right.
Much like a credit score, your sender reputation is also governed by multiple factors. The most important is your deliverability rate, followed by spam complaints. Overall engagement is part of the mix, as well. If your emails are largely ignored, your score will diminish, because it’s clear that the people on your list are not seeing value in your messages.
Other factors include:
- Email volume: Sending out bulk emails at too high a frequency can have a negative impact on your score.
- Content: Avoid using too much sales language.
- Authentication: Verifying your email account via email authentication protocols like SPF, DKIM, and DMARC can improve your sender reputation.
- IP Address Reputation: If spam has been sent from the same, shared IP address, your sender reputation may take a hit.
- Unsubscribe rate: Much like engagement metrics, your unsubscribe rate hints at a disconnection with your audience.
Make sure to keep an eye and take action on these areas to keep your sender score in the clear.
Use Double Opt-In
Using a verification system can help to reduce the number of invalid addresses that enter your list. However, these systems can’t necessarily detect when someone simply puts in the wrong email address — a valid account that belongs to someone else.
This is why using double opt-in is important. By sending out a confirmation email to new subscribers, you can check whether email deliveries are reaching the intended recipient.
An added benefit of the double opt-in process is that new subscribers confirm that they fully intend to sign up. This type of agreement helps you to stay within the limits of GDPR and CCPA.
It also ensures that everyone on your list actually wants to be there, making your email metrics and engagement data more meaningful.
Create Your Content Carefully
We touched on this before, but just to reiterate: be very careful about using sales language in your email campaigns.
It’s not that you can’t sell. Just steer clear of terms you might expect to find during a Black Friday shopping event:
- Buy now!
- Act fast!
- Limited time offer!
- Huge savings!
We would also recommend avoiding clickbait subject lines. While it’s fine to grab the attention or try something unusual, anything that misleads recipients could result in an uptick of unwanted spam reports.
Other content best practices include:
- Keep it simple: Use simple HTML and consistent fonts. Avoid special characters where possible.
- Don’t use too many images: The more photos you use, the higher your chances of reaching the spam folder.
- Go easy on the links: This is another trigger for spam filters.
In summary, create messages that look like regular emails rather than a sales brochure.
Use a Reputable Email Service Provider
With email service providers, you largely get what you pay for.
It’s not that all affordable services are bad. But cheaper options tend to attract the type of sender you don’t want to be associated with. If you’re sharing an email server with spammers, your deliverability rate could plummet.
When you’re selecting an ESP, check online reviews. Take a closer look at the security measures offered by each platform, and research deliverability rates. Good providers will put this information online, because they have nothing to hide.
Reduce Email Size
Let’s end our game plan with an easy step. Sometimes, bounce rates spike when you’re sending emails that are simply too big.
You can fix this issue by compressing attachments, and keeping the design simple. Aim to keep the total email size under 10MB, and the HTML under 100KB. If you really need to include a larger file, remember that you can always upload it to cloud storage and share the link.
Say Goodbye to Bounce Back
Seeing a deluge of email bounce messages arrive is not a good start to any email marketing campaign. However, it doesn’t have to be a disaster. As we have discovered in this post, rectifying a rising bounce rate or poor sender reputation is perfectly possible. You just need a clear action plan, and the right tools.
At the heart of it all is keeping your list clean and verified. NeverBounce offers an unrivaled set of tools for keeping your records perfect.
Our technology makes it simple to scrub invalid addresses and ensure future signups are legitimate. Why not give it a try today?