Hard vs Soft Email Bounces: The Differences and How to Avoid Them

Have you ever sent an email and shortly after received a notification saying it wasn’t delivered? Well, this is an email bounce. It can be incredibly frustrating.

There are numerous reasons why an email bounces. It could be because of a typo in the email address, a full mailbox, or a DNS failure. Whatever the cause, you’re going to want to get to the bottom of it.

In this article we’ll go into detail about the differences between email bounces, the reasons behind them, and how you can reduce your email bounce rate. 

What are Email Bounces?

Emails are considered ‘bounced’ when delivery fails. You’ll often receive an auto-response reply advising you the email has not reached its intended recipient. There are two types of email bounces: a hard email bounce and a soft email bounce.

Hard Email Bounce

email bounceWhen a hard bounce happens, it indicates a permanent delivery failure. This can happen for a number of reasons, including sending an email to an address that doesn’t exist (maybe the subscriber gave a false address or simply misspelled it), or the address isn’t accepting incoming mail. 

Another common reason is that the ESP (email service provider) has flagged your mails as spam or potential fraud. When this is the case, a hard bounce is recorded on your account every time it happens. Distributed spam attacks and email bombs are two common cybercrimes  that can result in a hard email bounce.

Soft Email Bounce

As the name suggests, this is a less serious type of bounce. It usually indicates a temporary issue such as the recipient’s inbox being too full to accept incoming mail. It could also be due to other issues such as the message being too large to be accepted or your ESP’s server timing out. The common thread is that soft bounces are viewed as temporary issues. 

Because these bounces are viewed as temporary, ESPs will retry delivery in most cases. However, your soft bounce will be changed to a hard bounce if several (usually three or four) attempts to deliver the mail fail, and no further attempts will be made. 

What are the Differences between Hard and Soft Email Bounces?

A soft bounce is a temporary issue.

The primary difference between a hard and a soft email bounce, as mentioned previously, is that a soft bounce is usually due to a temporary issue that is viewed as fixable. 

A soft bounce is fixable when you diagnose a problem.

In some cases, the issue that causes a soft bounce may be rectified. For example, the recipient may empty their inbox, thus allowing the email to be received on a later attempt. 

A hard bounce is a permanent failure you cannot fix.

Sadly, there is no immediate fix for a hard bounce. If you have been given the wrong address - either deliberately or accidentally - then there is little you can do to rectify things. 

What is an Acceptable Email Bounce Rate?

email bounce rateEmail bounce rates can vary according to the sector you operate in. If your email bounce rate is above 2%, then you should be taking some time to look into why a higher rate is occurring. It could be something as simple as you using a subscriber list that is old and possibly out of date. Keeping a low bounce rate should be a service goal as you want as many customers as possible seeing your emails. 

If you’re working in ecommerce, then your average bounce rates should be around 0.19% (for hard bounces) and 0.26% (for soft bounces). 

Causes of Email Soft Bounce?

Full inbox

If the recipient’s inbox is full, then it will automatically reject any incoming mail. It may also be that your email content is larger than the space remaining in an almost-full inbox. 

Automated content blocker

When the recipient (or the ESP) has an automated content blocker, then certain types or sizes of content may be automatically blocked. If this is happening a lot, then you can look at the content in your emails and change it. 

Incorrect recipient address

This can happen for a number of reasons. If the error lies at your end, it may be as simple as checking the address against your subscribers’ list. However, if the intended recipient has given you the wrong address, then there is little you can do. 

Nonexistent domain name

If you have a nonexistent domain name, there is not much you can do unless you are experiencing multiple errors with the same domain. In that case, you could reach out to the domain for assistance. 

Outdated email list

If you are using an old subscriber’s list, there is a chance that many of the email addresses could be unused now. You should look at updating email lists on a regular basis and ask subscribers to verify or update their contact info. 

DNS failure

This can be a tricky one as the error may be temporary or permanent. It could be as simple as the recipient’s email server being down or it could be more complicated in that typos have created issues. 

Message too large

If your emails contain large (or multiple) attachments, then the recipient may have a limiter on the size of emails they receive. It may also be the case that the ESP has a limit on the size of messages it will send or accept. 

Limit reached

Some ESPs place a limit on how many emails can be sent or received in a single day. If you find this is a regular reason for email bounces, then you may want to consider switching your ESP. 


This is an unusual type of bounce as you may get notification that it’s a soft bounce but the email has been delivered. It happens when recipients have auto-reply set up because they are away from their desk or on holiday. 

Causes of Hard Email Bounces

Recipient doesn’t exist

If the intended recipient has deleted their account or if they have given you a false email address, then there is nothing you can do. Your ESP will classify it as a hard bounce and make no further attempts to deliver the mail. 

Email blocked by server

With cybercrime on the rise, there are increased security measures put in place by ESPs, companies, and individuals. These measures, which include SPF, DKIM & DMARC, ensure that you are who you say you are. If a server flags your email as suspicious, then it will block you, resulting in a hard bounce. 

Mailbox is full

While this is initially a reason for a soft bounce, it will become a hard bounce if repeated attempts at delivery fail due to the inbox still being full. 

Challenge-response error

Although this can result in a hard bounce, it is a solvable problem. It happens when recipients (or ESPs) set up an additional firewall to authenticate the senders of emails. If it’s your first time contacting someone with this feature, you will be asked to verify your identity. Failure to do so will result in a hard bounce. 

Poor server reputation

This issue usually happens when there are many spam messages coming from the server. These may not be coming from you and could be due to hackers hijacking the server. You can prevent this happening by ensuring your mailboxes and servers are protected by a proactive, multi-layered cloud email security solution.

Email Sender Reputation Explained

sender repuationIf you send lots of emails, then ISPs assign you an email sender reputation. This is a score that reflects how trustworthy your organization - and the emails it sends - are. If you have a high score, then your emails should not encounter any major security issues. However, if your score is low, then you may find that you will have a lot of hard bounces. 

How do you protect your sending reputation?

  • Check your email lists regularly for addresses that may be out of date or that never respond. High bounce rates will lower your reputation score so this is a crucial task. 
  • Ensure your subscribers can see an opt-in policy. This can help verify that email addresses are valid but also highlights that they have given consent to receiving mail. 
  • Closely monitor your email delivery metrics. This can help you identify non-responders and potential invalid addresses. 
  • Differentiate between hard and soft bounces. The latter are usually solvable issues while the former usually indicates an issue that cannot be resolved. 
  • Don’t dive in the deep end. If you have a new account, build up sending volumes gradually. Security algorithms may flag your mails as spam if you immediately launch big campaigns. 

How is domain reputation calculated?

Many providers are guarded about the algorithms they use but your domain reputation score is like a credit score and has a 1-100 scale. While you may not know the algorithms, you can be aware of some of the factors that are taken into account when calculating that score:

  • Open rate.
  • Reply rate.
  • Reported spam rate. 
  • Read rate. 
  • Deleted without reading rate.
  • Identified as ‘not spam’ rate. 
  • Spam placement rate.
  • Click rate. 
  • Hard bounce rate. 

How to Improve Your Sender Score

If you find your score is low or has dropped, revisit some of the points mentioned in the protecting your reputation section. In particular, focus on the following:

  • Regularly carry out housekeeping on your email list and remove subscribers who never engage
  • Consider using email verification tools (or a double opt-in confirmation) to avoid incorrect addresses 
  • Never ever buy email lists; always build your subscribers list organically 
  • Stick to stated schedules and frequency
  • Research spam trigger words that may be flagged 
  • Keep content relevant so it isn’t flagged either
  • Use advanced security options to protect your email accounts. 

Tips on How to Avoid Email Bounce

If you follow the best practices listed in this article, you should see lower email bounce rates. There are a few other things you can do to avoid or reduce those bounce rates though. 

Don’t send marketing emails from a free mail service

While we all like to find ways of cutting costs, using a free email service such as GMail or Yahoo could actually cost you more in the long run. And you can still use such services for singular or low volume emails. But if you’re sending high volumes of marketing emails from one of these free services, then they are more likely to encounter content filters and other security features and you will see deliverability suffer. 

If you have a website, and you really should if operating online, then your web host should also provide email services and addresses. This should then give you a domain-based email address that will help improve reputation and deliverability. 

Make sure your domain is authenticated

A major factor in protecting your domain reputation is ensuring it is authenticated and it is essential for any SaaS app. This is a security measure that verifies any email from its point of origin and also checks emails to avoid or reduce the likelihood of spamming. 

Authentication has four basic steps:

  1. A business/organization establishes a policy for its outgoing emails.
  2. All email senders configure their email settings in order to comply with the policy.
  3. Emails received from the domain are then checked against the established rules
  4. The receiving server will then take action depending on if the email has been authenticated or not.

There are three main authentication tools you can use to ensure your emails are delivered without a problem:

spf dkim dmarcSPF: This stands for sender policy framework. It verifies the sender of an email and fights against impersonation. 

DKIM: This is a tool that adds a digital signature to an outgoing email. This allows servers to verify that the message hasn’t been altered or tampered with.

DMARC: This tool combines SPF and DKIM and allows you to check if the “from” address in the email matches the address the email is coming from. You can also decide what to do if an email is flagged as suspicious: is it rejected, sent to spam, or is no action taken?

If your domain is authenticated, then any emails you send should transfer more smoothly through spam filters and other security measures and be delivered safely to the recipient's inbox. 


Email remains a strong and effective method of business communication; however, a large amount of emails sent every day are spam. In fact, in December 2021, 45.37% of all emails sent were classified as spam. There are also more robust security measures designed to identify and filter out spam, so a cautious approach to sending emails is essential. 

Of course, you also need to consider how secure your email accounts and servers are. Having a robust email security solution can guard against malicious hackers and cybercriminals attempting to hijack your accounts, something that could damage your reputation severely. 

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