Email Bounce Backs — The Complete Guide for 2020

April 7, 2020
Written by Salman

The success and long-term survival of any business today is heavily reliant in their ability to conduct impactful email marketing campaigns. However, as with everything else in life, conducting an email marketing campaign is no easy job. That difficulty is compounded by the fact that you will encounter email bounce backs; which are perhaps the most significant obstacle for any email marketing campaign.

Statistics show that in 2019, 8.85% of the total emails sent got bounced. Which is not a good number considering that the benchmark for what is an acceptable bounce rate is 2%.

It's no surprise that the internet is filled with people who are desperate to find the answers to questions like “how to stop email bounce backs?” or “how to fix email bounce backs?”

If your marketing campaign is currently struggling with email bounce back issues and you are seeking a solution, you’re at the right spot. In this article, you will find everything there is to know about email bounce backs in 2020. Everything from basics like what an email bounce back is to how you can reduce and eliminate bounce backs will be covered below.

Let’s start with the basics.

‘Email Bounce Backs’ — What Are They?

In the simplest of terms, an email bounce back is when the emails you send cannot reach their intended recipient. It’s quite self-descriptive.

An ‘email bounce-back message’ is the message you get from the automated email system that lets you know that your message has not reached the recipient. It is also known as a ‘bounce message’ or sometimes just a ‘bounce’. There are of course, more formal, technical terms for bounce messages. These include "Non-Delivery Report" or "Non-Delivery Receipt" (NDR), [Failed] "Delivery Status Notification" (DSN) message, or a "Non-Delivery Notification" (NDN).

In most cases, we hear cases of Gmail bouncing back emails or emails bouncing back in Outlook. This is not due to any fault in Gmail or Outlook. It's just that they happen to be the most used email clients. Email bounce backs are a problem that is prevalent across all email clients. Something that must be understood is the fact that the mail client in and of itself will never be the reason for your emails not reaching their destination.

So, now that we know what an email bounce back is, we need to know how we can identify an email bounce back from the many other potential issues you might face while conducting an email marketing campaign.

Identifying Email Bounce Back Messages

Thankfully, it’s not hard to identify email bounce back messages. They usually look like this:

email bounce back message
A typical bounce back message.

Thankfully, you will find that bounce messages will contain several pieces of important information that can help you understand exactly why your message was not delivered:

  • The date and time the message was bounced,
  • The identity of the mail server that bounced it,
  • The reason that it was bounced (e.g. user unknown or mailbox full),
  • The headers of the bounced message,
  • Some or all of the content of the bounced message, and sometimes
  • Recommendations to fix the bouncing issue

For those who are interested in more technical details, RFC 3463 describes the codes used to indicate why emails bounce. Common codes are 5.1.1 (Unknown user), 5.2.2 (Mailbox full) and 5.7.1 (Rejected by security policy/mail filter).

Bounce messages in SMTP will also be sent with the envelope sender address <>, which is known as the null sender address. More often than not you will also find that they are sent with a "From:" header address of MAILER-DAEMON at the recipient site.

Of course, if the bounce back message contains recommendations, your first course of action should be to try them. Else if you know what mistake you might have made, you can rectify it and send the email again. If the second attempt is not successful, no worries. Read on.

The bounce back message that is most often seen is “Delivery to the following recipient failed permanently”. You will receive this message under the following conditions:

  1. The recipient’s email address does not exist
  2. The email address is either misspelled or contains a typo
  3. There are unnecessary spaces in the email address

The Three Types of Email Bounces — Hard, Soft & General

There are three variations of email bounce backs: hard bounces, soft bounces and the less common general bounces. Knowing the distinction between these three is critical if you want to solve your bounce back issues.

Hard Bounces

These are instances where your email has been completely rejected, for whatever reason. This could be due to the fact that your recipient’s email address does not exist anymore. Or alternatively, the email domain name has been shut down. At times, this can also happen if you’ve misspelled the email address. The biggest concern about hard bounces are that they are usually permanent problems and cannot be fixed from your end. If you get a hard bounce due to a reason other than a spelling error, you are better off discarding that specific email address.

Soft Bounces

As the name may imply, these are not anywhere near as worrisome as hard bounces. Soft bounces are mostly caused by temporary problems. These problems can include the receiving mail server not responding or their mailbox being full. If this is the case, the bounce back message will state the reason. In many cases, the reasons behind the soft bounce will have fixed themselves automatically; you can send your email without any issue after some time.

General Bounces

General bounces are not as severe as hard bounces, but they will also probably not solve themselves like soft bounces. They can happen when a firewall exists on the server that prevents them incoming email from outside their network. This is a common occurrence when the email address belongs to a corporation that does not allow incoming emails from outside or unknown sources. More often than not, the only way to fix this issue is to get in touch with the owner of the network and ask them to allow your emails through.

Email Bounce Backs — Why You Should Be Concerned About Them

It might seem like email bounce backs are nothing you should worry too much about. After all, if the email doesn’t go the first time, you can always try again, right? — there are actually reasons why you should be concerned if your email marketing campaign has a high bounce rate.

Email bounce backs have a significant negative impact on both your IP reputation and your deliverability. Both of these measure a number of factors. For example: how many emails are actually delivered, how many are caught by the spam filter, how your recipients feel about your email, and more. Every bounce back or bad email that you send will give your business a negative score.

Then, of course, you also need to be aware of your sender reputation score. Your sender reputation score will take a hit every time you send out an unwanted email or an email that bounces back. It is not an easy task to build a positive sender reputation but it is quite easy to ruin it. Just repeatedly bouncing emails can do it.

In the worst case scenarios, you can even have your email suspended by your Email Service Provider (ESP). This can happen if you exceed the benchmark set by your ESP for spam, unnecessary emails and bounce backs.

It boils down to this: if you keep getting emails that are bouncing back — whether it is hard, soft, or general — your business’ credibility will take a hit. Your email marketing campaign will fail. You need to avoid that by keeping a keen eye on your marketing campaign. When you see that a particular email address is not responding, you need to deal with. Make the changes necessary. Scrub your email list, verify the addresses and so on.

Of course, to make the changes, you need to know why your emails might be bouncing back in the first place.

Reasons for Email Bounce Backs

There are many potential reasons for email bounce backs. One common reason is the recipient address is misspelled, or simply not existing on the receiving system; which is known as a user unknown condition. Other reasons may include lack of space on the receiving end of spam filters blocking the message. There are also cases where a mail client will allow users to "bounce" a message on demand. However these, unlike the automated bounces, are not real bounces.

Let’s look at some of the possible reasons for your email bouncing back.

1. Invalid Email Address

As we’ve already mentioned, invalid email addresses are one of the most common reasons. In such cases, your email service provider has no option but to bounce the email. The bounce back message will let you know it is a “non-existent email address”. In most cases, this falls under the category of hard bounces.

More often than not, this issue can be traced back to you using unverified emails. This can be because you bought email addresses in bulk or used an outdated email list. Some other possibilities include there is a typographical mistake in the email address, the use of an invalid email format, or the owner of the email address leaving their organization (in cases of company emails).

You can’t count out someone having purposefully left an invalid email address on purpose. It’s an unfortunate fact that people often use fake email addresses when they’re signing up for a service for one-time use or when you’re offering something in exchange for an email address.

If you face this issue, you should recheck the email address for typos or see if you have another way to contact your intended recipient. You should never be repeatedly sending emails to invalid email addresses.

2. Undeliverable Emails

If your email cannot reach your recipient because the email server is 1) not currently available or 2) is overloaded, it is considered an undeliverable email. In such cases, the recipient’s server is not be able to receive any incoming requests. Your email ends up bouncing back.

If a server is temporarily unavailable, it is most likely because they have crashed or are under maintenance. If they are overloaded, it means that they are dealing with one too many requests all at once. The good news is that in both cases, the bounce back is categorized as a ‘soft bounce’. You just have to wait a while before sending the email again.

Keep in mind that undeliverable emails can also fall under the ‘hard bounce’ category if the email server cannot be found at all. Which can happen if the server has been shut down.

If you’re having bounce back issues due to undeliverable emails, the best course of action is to try sending the emails again after a short period. If the bounces continue, strike the email out of your mailing list and proceed.

3. Full Inbox

Every mailbox has an allocated quota. This can be measured either by the number of emails or their size. Whatever the case, if your intended recipient’s inbox has met its allocated quota, your emails will be bounced.

Thankfully, this is a relatively rare issue. It usually happens when the email address is active but doesn’t have free space to take new emails. Further, this is also considered a ‘soft bounce’ and as such, it’s only a temporary issue.

When your email doesn’t go through because of a full inbox, you should try again after a few days. It will more often than not have sorted itself out. There can also be instances where the contact has abandoned that particular email address, meaning that the inbox won’t ever be cleaned again. As always, proceed with caution and abandon the email address if the bounces repeat. You can always try and contact your intended recipient via another method.

4. Blocked Email/IP Address

You may also find that your emails are bouncing back because your email/P address has been blocked. It could be caused by the receiving server blocking your email or by the recipient’s email service providers blocking IP addresses that they suspect of spamming activities. In either case, your emails will not be able to reach your intended recipient’s server, resulting in an email bounce back.

When it’s the first scenario — the server has blocked your email — it is most likely because the email address is associated with large corporations, government entities, schools and the like. As these organizations are all quite strict about both incoming and outgoing emails, they will block all emails that are not part of their internal network.

So what happens in the second scenario, where an ESP has blocked your IP address? The thing is that free email providers like Gmail, Yahoo, Zoho, Outlook, AOL all share one IP address with many users. When one of these shared users conducts a spam-filled email campaign, other email users who share the same IP address will also get affected. You could be doing everything right and still get affected if you are using a free email.

There is a workaround for the first case. Get in touch with the organization and ask them for an exception for your email address. As to the second case... Well, just don’t use free emails to conduct your email marketing campaigns.

5. Vacation/Auto-Reply

Your emails could also bounce if your intended recipient is not available to access their email for whatever reason (usually vacation) and has set up an auto-reply. In such cases, your emails will bounce back and the bounce back message will state the reason.

Thankfully, while this is considered a bounce back, it is neither a hard bounce nor a soft bounce and it will not affect your email deliverability or sender reputation score. After all, an auto-reply still means that the email has actually reached its destination.

However, this is still an issue that you should keep your eye on. There could be instances where an email address that is abandoned has an auto-reply set up. If a particular email address continues to give your bounce backs over a long period of time, remove it from your list.

6. Email Size Too Large

Another important factor for email bounce backs could be your email’s size. In most cases, your email client will have a certain max size allowed. Think, for example, of something like Gmail’s 25mb limit for attachments. Much like that, there are email service providers that restrict the size of emails, for any number of reasons. There are also some email service providers that allow only text emails.

In either case, if the email you send is either too large or contains images where only text is allowed, your emails will bounce back. This is why it’s very important that you make sure that your emails are as optimized as possible and work equally well without images.

7. Low Sender Reputation Score

We’ve already talked about the sender reputation score and why it is important. Understandably, if your sender score is low, your email could be automatically routed towards the spam filters. Or simply cause a bounce back. It's a paradoxical problem for most email marketers. This situation will only further decrease your sender reputation score and increase your overall bounce rate.

How do you deal with it? Make sure that your sender reputation score has no reason to reduce in the first place by keeping on top of things.

8. Other Reasons

We can break down some of the reasons why your emails could bounce back, we can’t track all on one article. This means that you could encounter a bounce back message stating a reason that we’ve not looked at. Or, you could encounter a bounce message that shows no reason.

If there are no reasons given, all it means is that there are things that are too technical. In such cases, make sure you monitor the specific addresses that cause the bounce. See if there is a recurring issue. If there is, take action so that your overall campaign isn’t affected.

How to Decrease Email Bounce Backs

Once you know the cause of something, the next step is to learn how to fix it, right? So, now to answer the question of “how to reduce email bounce back?”

Before we go any further, however, let us get the bad news out of the way first. If you are conducting an email marketing campaign on a large scale, eliminating email bounce back entirely is near impossible. To begin with, there are just way too many emails involved. Then you have to consider that new email addresses will be added every single day as the campaign spreads and expands. So if you aim to completely get rid of email bounce backs, we’re sorry to tell you that you can’t.

But the good news is that you can reduce the number of bounce backs and get them under the recommended benchmark.

Which leads us to two important questions we need to consider:

  1. What is the recommended benchmark?
  2. How do you calculate email bounce rate?

The answers to these two questions will serve as an excellent starting point to reducing your bounces. They will also help you get a solid measure of exactly how much success you are having with your marketing campaign. It will also help you make important decisions as your campaign grows and changes.

Recommended Benchmark for Email Bounce Rates

If we are to go by Epsilon’s Email Trends and Benchmark guide (2010), the average bounce rate for commercial emails can be anywhere between 2% and 15%. That information is obviously out of date.

According to Campaign Monitor’s 2020 Global Email Benchmarks Data, the average bounce rate is 0.7% across all industries. The recommended benchmark for bounce rates is less than 2%.

If you are having more than 2% of your emails bouncing, it’s time for you to look into what’s going on with your campaign. If you have a bounce rate of over 5% or perhaps 10%, it can very well be a sign of a significant problem with your campaign that you need to act on immediately.

It’s also important that you know that each industry has its own average bounce rate, so you don’t need to fret if your bounce rate isn’t a perfect 0.7%. For instance, the Construction, Contracting and Manufacturing industry has a bounce rate of 2.2%. If you are in the same industry and are seeing similar bounce rates, it’s nothing for you to worry about. You can always try to improve, of course.

So, keep in mind the average acceptable bounce rate — 2% — but also know the number for your specific industry. It will serve as a guide in your own email marketing campaign as to what percentage of bounces you should accept.

Calculating Email Bounce Rate

There is no need for you to manually calculate your email bounce rates today. After all, any email marketing client that you use will give you the number along with a smorgasbord of other data. Still, it’s not complex math and you should at least know how it is calculated.

  1. Take the total number of emails that have bounced.
  2. Divide the number by the number of total emails you sent out.
  3. Multiply the number by 100 to get the bounce rate.

Let’s put that into action.

Say you’ve sent out 10,000 emails, of which 350 bounced.

150 / 10000 = 0.15

‘0.15’ means that for every email you sent, 0.35 bounced. Now, multiply that number by 100 for the percentage.

0.35 * 100 = 1.5

So in this scenario, you’d have a bounce rate of 1.5%. Which is quite a good bounce rate and comfortably under the acceptable rate of 2%.

Now that we know what an acceptable bounce rate is and how bounce rates are calculated, our next focus should be on how you can reduce your bounce rates and bring them well under the acceptable bounce rates.

Decreasing Email Bounce Backs

When you’re setting out to decrease email bounce backs, there are obvious steps to take. If your mailing list is old, chances are that a number of the email addresses in there are out-of-date or invalid. Of course, you should clean your email list with an email validation service, but there are steps that you can take yourself before hiring a third-party company to help you out.

1. Double Opt-In

Double opt-in is the first method you need to implement. Because it is pretty much the best method for building a valid email list.

When you use the single opt-in method, it’s straightforward. Someone enters their email, their details and they submit. The email will automatically be added to your mailing list. There is no hassle here.

However the double opt-in method has one additional step that might be a little bit annoying for people who legitimately want to be on your mailing list, it will be better for you in the long run. In the double opt-in method, once a user registers with your mailing list, they get an email asking them to verify their account. Only after they verify do you add them to your mailing list.

This extra step ensures that they are an actual user and not a bot or someone using fake email. After all, a bot can’t engage by clicking a verification link and if it’s a fake email, they would never get the verification email. With just one added step, you can reduce email bounce rate drastically.

2. A Good Sign-Up Form

Seeing as how email marketing is entirely based on sending emails out to contacts, you need a good sign-up form. Ideally, you want to go for an online form instead of an actual paper form. This allows you to prevent human error both on your part and the user’s part. Typos, for instance, will be mostly eliminated when you are using a web-based form.

With an excellent sign-up form, you have the best place to gather valid contacts for your mailing lists. You can and should add a Captcha system into your sign-up form to prevent bots from signing up and if you’ve already got a double opt-in system in place, you’re good to go.

3. Clean and Up-To-Date List

It should be obvious that you need to make sure that you keep your mailing list clean and up-to-date. Email addresses often expire with time and that will only lead to increased bounce rates. Using an email validation service to keep your list verified and clean is good for the health of your email marketing campaign, but you can also go one step further.

Include a method that allows the people on your mailing list to update their information and verify that the information is correct and up to date. Just the simple act of including a link to a form that allows them to update their own information can go a long way in keeping you one step ahead of a potential bounce back issue.

4. Double-Checking

As good as machines are — and they are pretty good — there is nothing wrong with double-checking manually. Double-checking is especially important if you are manually building a list.

Make sure that useless emails like [email protected] or [email protected] are not present on your list. Make sure that ‘Yahoo’ is spelled correctly, instead of being spelled like ‘Yahooo’. If it’s a common name, make sure the spelling is correct. Just a few minutes double-checking will help you prevent any potential issues.

4. Authenticated Email Account

Having an authenticated email account can go a pretty long way with reducing email bounce back rates. Email account authentication is a process that is done to maintain your sender reputation, which in turn will help reduce email bounce back rates. There are three types of authentication processes to improve your email deliverability.

  • SPF
  • DKIM
  • DMARC

For those who want to know more about email authentication:

  • SPF allows senders to define which IP addresses are allowed to send mail for a particular domain.
  • DKIM provides an encryption key and digital signature that verifies that an email message was not faked or altered.
  • DMARC unifies the SPF and DKIM authentication mechanisms into a common framework and allows domain owners to declare how they would like an email from that domain to be handled if it fails an authorization test.

These procedures help the recipient’s server to check the authenticity of the email received. When the receiving server sees that your email is authenticated, they provide a clean chit to your message, let it go through and ultimately reduce your email bounce rate.

5. Avoiding Spam

We shouldn’t have to tell you this, but don’t make your email look like spam, don’t add words that might trigger spam filters, and certainly don’t go and actually spam.

Email service providers implement spam filters to provide a better user experience. But with spammers constantly evolving their tactics to make their emails look as legitimate as possible, you need to be proactive to make sure your emails are never mistaken for spam.

Steps to follow to avoid spam include:

  • Avoid overusing words like “FREE”, “50% OFF”, “OFFER” in your emails. Spam filters often categorize emails that frequently use such terms to be spam.
  • Don’t have too many links in your email, which can make spam filters suspect you of conducting phishing activities.
  • Maintain a content ratio of 60:40 text to HTML. Rich graphics and beautified HTML emails are usually promotional and plain text emails are boring.
  • Don’t overuse and if possible, avoid using CAPS, BOLD and Exclamation marks. These are seen as signs of spam emails.

Following the above pointers are just some of the ways you can ensure that your emails don’t fall trap to any spam filters. You can and should also use tools like mail-tester.com, isnotspam.com, and email-checker.net to see how similar your current email marketing campaign materials are to spam.

If they’re not, great. If it is, you can take pre-emptive action and make sure that your email reaches your potential customers.

6. Scheduled, Consistent Emails

Maintaining a consistent mailing schedule is another way you can ensure that the number of bounce backs reduces. If you have a schedule that is based on benchmarked engagement patterns of your industry’s customers, you stand to gain two benefits. First, you have a fixed plan for your own campaign. Second, your emails are expected by your customers, which can in fact increase open rates.

You should also make sure that you maintain some time gap between two consecutive emails in your email marketing campaign. Email service providers’ algorithms know that no human can send multiple different emails in one go. If it happens, the algorithms will assume it to be bot activity and this can cause your emails to bounce or end up in the spam folder.

The ideal gap between two consecutive emails is estimated to be around 90 seconds. If you’re using an email automation tool — which you should — you can set it up to send emails with the right gaps of time in-between them.

7. Don't Exceed Daily Email Sending Limits

Every email service provider has a certain email sending limit in place. You should not exceed your daily limits. When you try to do that, you will start facing email bounce back issues.

Make sure you know how many emails you are allowed through your email service provider and adjust your schedule accordingly. Exceeding the daily limit frequently is not recommended at all, as it will lead to your account being permanently blocked.

8. Avoid Free Sender Domains

We’ve already talked about why you should not use a free email sender domain (e.g., @gmail.com, @outlook.com, etc.). It’s because the IP addresses are shared and you could be affected by the actions of another user. But on top of that, with free email sender domains, you are also not allowed to authenticate your email account.

This will, of course, make the emails you send from your account more likely to get caught in spam filters and lead to an increase in your email bounce rate. So always use an authenticated business domain for your email marketing campaigns.

9. Monitor Sender Reputation Score

We’ve already talked about the sender reputation score. The standardized value provided to the domains to check their email activities. If you have a low sender reputation, it can lead to your emails bouncing back, going to the spam folder, or sometimes even your account being outright blocked.

In addition to following and implementing the other methods in your email marketing campaigns, you should always keep an eye on your sender reputation score. Using a tool like Sender Score is great help in that regard. Make sure everything is positive there and your email marketing campaign will proceed without too many hiccups.


Following all the steps above will give you a solid base to build off from. They will help you increase your sender reputation, your IP reputation, and your deliverability scores and help your marketing campaign grow.

But in addition to taking those steps, you should also consider hiring services that exist for the sole purpose of making the email marketing process as easy as possible for you...

Email Validation Services

Sometimes the simplest answer to the question “how to fix email bounce back?” is the use of an Email Validation Service.

An Email Validation Service provides a crucial service to anyone who is doing marketing via the internet. Email validation services, which are sometimes also known as email list cleaners, go through all of the email addresses on your list, find contacts who could cause bounce backs and remove them from your mailing list.

Anything that the email validation service deems unfixable, it will delete. This includes things such as nonexistent emails, obviously fake emails, invalid names and more. If the email validation service thinks you can take action to fix the issue (with typos or contacts on vacation), it will mark the relevant contacts so you can take action.

Invalid addresses on your email list can severely damage your brand. In fact, data shows that even if invalid addresses constitute only 10% of your email list, only about 44% of your emails are likely to get delivered. This is an issue you can easily avoid by using an email validation service.

One such Email Validation Service is VerifyBee.

VERIFYBEE

VerifyBee is one of leading email validation services that is built to make sure that your message is received. After all, even the world’s best message won’t matter if there is no one to hear it.

The VerifyBee platform has been designed to make the email verification process as simple and straightforward as possible for you. Using the cutting edge techniques such as Spamtraps, Risk Validation, SMTP Validation, MTA Validation and Syntax Verifiers and more, we provide service that will ensure a completely clean list. And what’s more? Unlike other platforms we actually ping servers to verify each and every email on your list for the most accurate results.

We do everything that every other service does. We closely monitor your bounce rates and give you a suite of tools that will allow you to deal with any issue that may arise. VerifyBee safeguards your email marketing campaign from limits set by internet regulators for bounces, spam complaints and unsubscribe requests.

Our platform is also designed to integrate with major email marketing tools such as MailChimp, Platformly, Aweber Moosesend, Mailshake, and Lemlist. You can connect any of these services to VerifyBee with incredible ease and continue your work, uninterrupted.

We also believe that everyone deserves quality email validation services that won’t break your bank. As such, our services are affordable while still maintaining the same quality as any other email list cleaning service on the market.

With incredible pricing and cutting edge email list cleaning techniques, VerifyBee provides you with the best value for money and the biggest return on investment when it comes to email list validation. Sign up now and get started on reaching new levels of success with your email marketing campaign.

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