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 a typo in the email address, a full mailbox, or a DNS failure. Whatever the cause, you will want to get to the bottom.

In this article, we'll detail the differences between email bounces, their reasons, and how to understand why they happen.

What are Email Bounces?

Emails are considered 'bounced' when delivery fails. You'll often receive an auto-response reply advising you the email has yet to reach its intended recipient. There are two email bounces: a hard and a soft email bounce.

Hard Email Bounce

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

email bounceAnother common reason is that the ESP (email service provider) has flagged your emails as spam or potential fraud. When this `happens, 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 severe 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 problems, 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 usually retry delivery. 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.

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

A soft bounce is fixable when you diagnose a problem.

Sometimes, 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 deliberately or accidentally give the wrong address, there is little you can do to rectify things. 

What is an Acceptable Email Bounce Rate?email bounce rate

Email bounce rates can vary according to the sector you operate in. If your email bounce rate is above 2%, then you should be looking into why a higher rate is occurring. It could be as simple as using an old and outdated subscriber list. Keeping a low bounce rate should be a service goal, as you want as many customers as possible to see your emails. 

If you're working in e-commerce, your average bounce rates should be around 0.19% (for hard bounces) and 0.26% (for soft bounces).

What Are Causes of Soft Email Bounces?

Full inbox

If the recipient's inbox is complete, 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, 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 several 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 you can do little. 

Nonexistent domain name

If you have a nonexistent domain name, there is only little you can do unless you are experiencing multiple errors with the same domain. In that case, you could reach out to the field for assistance. 

Outdated email list

If you use an old subscriber list, many email addresses could be unused now. You should look at updating email lists regularly and ask subscribers to verify or update their contact info. 

DNS failure

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

Message too large

If your emails contain large (or multiple) attachments, the recipient may have a limit 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 limit how many emails can be sent or received daily. If this is a regular reason for email bounces, consider switching your ESP. 


This is an unusual bounce, as you may get a 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. 

What Are Causes of Hard Email Bounces?

The recipient Doesn't Exist

If the intended recipient has deleted their account or given you a false email address, 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, 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. You'll be asked to verify your identity if it's your first time contacting someone with this feature. Failure to do so will result in a hard bounce. 

Poor server reputation

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

Email Sender Reputation Explained

sender repuation

If you send many emails, ISPs assign you an email sender reputation. This score reflects how trustworthy your organization - and the emails it sends - are. Your emails should not encounter significant security issues if you have a high score. However, if your score is low, you will have many hard bounces. 

How do you protect your sending reputation?

  • Check your email lists regularly for addresses that need to be updated or never respond. High bounce rates will lower your reputation score, so this task is crucial. 
  • Ensure your subscribers can see an opt-in policy. This can help verify that email addresses are valid and highlight that they have consented to receive 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 indicates a problem 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 emails as spam if you immediately launch extensive campaigns. 

How is domain reputation calculated?

Many providers are guarded about their algorithms, but your domain reputation score is like a credit score with 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 your score is low or has dropped, revisit some 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 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 faded, either
  • Use advanced security options to protect your email accounts. 

Tips on How to Avoid Email Bounces

If you follow the best practices listed in this article, you should see lower email bounce rates. You can do a few other things 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 to cut costs, using a free email service such as Gmail or Yahoo could cost you more in the long run. And you can still use such services for singular or low-volume emails. But suppose you're sending high volumes of marketing emails from one of these free services. In that case, they are more likely to encounter content filters and other security features, and deliverability will suffer. 

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

Make sure your domain is authenticated

A significant factor in protecting your domain reputation is ensuring it is authenticated, which is essential for any SaaS app. This security measure verifies any email from its point of origin and 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 to comply with the policy.
  3. Emails received from the domain are then checked against the established rules.
  4. The receiving server will then act depending on whether the email has been authenticated.

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

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

spf dkim dmarc

DKIM: This tool 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, your emails should transfer more smoothly through spam filters and other security measures and be delivered safely to the recipient's inbox. 

Keep Learning About Securing Business Email

Email remains a strong and effective method of business communication; however, many emails sent daily are spam. In December 2021, 45.37% of emails 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 must also consider your email accounts and servers' security. A robust email security solution can guard against malicious hackers and cybercriminals attempting to hijack your accounts, which could damage your reputation severely. 

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