Understanding Hard vs Soft Email Bounces to Enhance Delivery Rates

Paying attention to why email bounces happen could help to diagnose an underlying problem with your inbox. They are also a factor in your sender reputation, which is essential for everyone doing online business. In this article, we'll detail the differences between hard and soft email bounces and what you should do to maintain email protection for your company.

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 bounce types: a hard and a soft email bounce. 

Hard Email Bounce

Hard email bounces indicate a permanent delivery failure due to sending an email to an address that either doesn't exist (perhaps a result of misspelling) or isn't accepting incoming mail. An Email Service Provider (ESP) may have flagged your emails as spam or potential fraud, and these bounces are recorded on your account every time they occur. Denial of service attacks and email bombs can cause a hard email bounce.

Soft Email Bounce

Soft email bounces indicate a temporary issue preventing the message from being sent. They could mean that a recipient's inbox is too full to accept incoming mail, that the message is too large to be accepted, or that an ESP server timed out. Since these bounces are only for a short time, ESPs will attempt a re-delivery. If delivery fails repeatedly, the ESP redefines it as a hard bounce, because it could be a potential threat to the server. Then, no further attempts will be made.

What are the Differences between Hard and Soft Email Bounces?

• Soft bounces are a temporary issue - As mentioned, soft email bounces are fixable issues, whereas hard email bounces are permanent problems. 
• Soft bounces can be fixed when you diagnose a problem - Soft email bounce conflicts can be rectified by the recipient emptying their inbox or adjusting other issues in order for the message to be received on a later attempt.
• Hard bounces are a permanent failure you cannot fix - Unfortunately, hard email bounces are not fixable, and little can be done to care for them.

What is an Acceptable Email Bounce Rate?

One of your company’s service goals should be to ensure that your email bounce rate stays below 2%, as anything higher is considered an issue for your sector. The rate can vary, but you should be concerned the second they go above the rates predicted for your company. For example, in e-commerce, your average bounce rate should be around 0.19% for hard bounces and 0.26% for soft bounces.

What Are the Causes of Soft Email Bounces?

• Full inbox - If there is no room left in the recipient's inbox to receive the message, or the message is too large for the space left, any incoming mail will be rejected.
• Automated content blocker - When the recipient (or the ESP) has an automated content blocker, certain types or sizes of content may be automatically rejected. Take a look at the information in your email and edit it so that it will be accepted.
• Incorrect recipient address - This is a fixable issue if it resulted from a mistyped address, but if you wrote it correctly and it still won’t send, there is not much that can be done.
• Nonexistent domain name - If you send to a nonexistent domain name, reach out to the field for assistance so that you don’t experience even more errors within the server.
• Outdated email list - Ensure you update your email lists regularly and have subscribers verify their information to guarantee that you only send messages to active accounts.
• Domain Name System (DNS) failure - This could simply result from the recipient's email server being down or typos causing problems for the server.
• Message too large - The recipient or their ESP may have a limit on the size or quantity of attachments they receive, which could prevent a message from being delivered.
• Limit Reached - Some ESPs limit how many emails can be sent or received daily. If you encounter this issue with your ESP, continue switching.
• Autoresponder - Sometimes, you may receive a notification that a message soft bounced even though the email went through to the recipient. This could happen when recipients have auto-reply set up since they are away from their desks or on holiday.

What Are the Causes of Hard Email Bounces?

• Recipient doesn't exist - If the intended recipient has deleted their account or given you a false email address, your ESP will classify it as a hard bounce and make no further attempts to deliver the message. 
• 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, and  DMARC email authentication procedures, ensure that you are who you say you are. However, if a server notices suspicious activity through email fraud detection mechanisms, it may reject the message and classify the delivery as a hard bounce.
• Mailbox is full - A full mailbox is only a soft bounce until repeated delivery attempts continue to fail.
• Challenge-response error - This happens when recipients or ESPs set up an additional firewall to authenticate email senders. You'll be asked to verify your identity if it's your first time contacting the recipient, and failure to do so will cause the message to be processed as a hard bounce.
• Poor server reputation - Messages may be rejected if a server constantly receives spam messages from you or hackers who hijacked the system. You can prevent such issues by protecting your secure email and servers with a comprehensive cloud email security software solution.

Email Sender Reputation Explained

If you send many emails, Internet Service Providers (ISPs) assign you an email sender reputation score reflecting your organization’s trustworthiness. Higher scores will have few significant email security issues, while low scores will result in many hard email bounces. 

How do you protect your sending reputation?

• Check your email lists regularly and determine which ones need updating or never respond. High bounce rates will lower your reputation score, so refining your list will keep bounces from happening as frequently. 
• Ensure subscribers can access the opt-in policy to verify email addresses and highlight their agreement to receive email. 
• Closely monitor your email delivery metrics to identify non-responders and potentially invalid addresses. 
• Differentiate between hard and soft bounces to determine what is a solvable issue and an unfixable problem.
• 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 guard their algorithms, but your domain reputation score is similar to a credit score with a 1-100 scale. Here are some factors to consider when calculating your company’s score: open rate, reply rate, reported spam rate, read rate, deleted without reading rate, identified as “not spam” rate, spam placement rate, click rate, and hard bounce rate. 

How to Improve Your Sender Score

If your score is low or has dropped, 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. 
• Build your subscriber emails organically and avoid buying lists.
• Stick to stated schedules and frequency.
• Research spam trigger words that may be flagged.
• Keep content relevant so it isn't flagged.
• Use advanced email threat security options to ensure email protection.
• Remember the “How do you protect your sending reputation?” suggestions.

Tips on How to Avoid Email Bounces

Follow these email security best practices to reduce email bounces, improve deliverability, and strengthen your sender reputation. Here are a few things to prevent high bounce rates:

Don't send marketing emails from a free mail service

Using Gmail, Yahoo, or any other free email software might result in your messages going through content and email filters, email protection features, and anti-spam services, all of which can harm your deliverability. There are various ways to send messages.

Suppose you have a website or operate online. In that case, your web host should also provide email addresses that give you domain-based email accounts that will improve your reputation and deliverability. 

Make sure your domain is authenticated

Any Software as a Service (Saas) app requires domain reputation protection through authentication measures, verifying any email as it travels from the sender to the receiver, reducing the chances of spam.

Authentication has four basic steps:

A business/organization establishes an email security policy for its outgoing emails.

All email senders configure their email settings to comply with the policy.

Emails received from the domain are then checked against the established rules.

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 secure emails are delivered without a problem:

• Sender Policy Framework (SPF) provides impersonation protection and fights against phishing attacks by verifying the sender of an email.
• DKIM adds a digital signature to an outgoing email, allowing servers to verify that the message hasn't been altered or tampered with.
• DMARC email authentication combines SPF and DKIM and allows you to check if the "from" address in the email matches the listed email address, permitting you to flag emails as suspicious.

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

Email Bounces and Deliverability FAQ

To resolve email deliverability issues, you've got to understand how bounce data affects sender reputation and what metrics are worth monitoring. The answers below help clarify these common problems:

Why do email bounces matter?

Email bounces affect the success of future email campaigns. ISPs and ESPs look at email bounce rates when evaluating your sender reputation. Too many bounces can reduce inbox placement, increase spam filtering, and make your server look untrustworthy.

Should I keep retrying bounced emails?

It depends on why the delivery failed, but you generally don’t have to. Keep in mind that soft bounces are automatically retried by ESPs until they are classified as a hard bounce. Retrying won’t work unless you check the problem. If delivery failed due to a misspelled address, simply correct the address. In the case of spam or reputational issues, the solution will be more involved.

What should I track in bounce reports?

Review both your hard and soft bounce rates to understand whether delivery failures are permanent or temporary. In addition, monitor SMTP error codes, spam complaint rates, open rates, click rates, spam placement, and sender reputation metrics. Together, these indicators identify patterns that may be affecting deliverability.

Preventing Email Bounces Improves Email Security

Email bounces are a delivery problem first, but they can also highlight bigger issues with your email setup. Old addresses, failed authentication, poor sender reputation, or a compromised account. All of these could cause messages to be rejected. When that keeps happening, legitimate email starts landing in spam or does not arrive at all. 

The same controls that improve delivery also help reduce the chance of a BEC scam or email account takeover. SPF, DKIM, DMARC, account monitoring, and sensible mail filtering make it harder for someone to impersonate your domain or use a compromised mailbox to contact customers and employees.

Managing bounces protects your company’s online reputation. Always keep your mailing lists clean, watch bounce reports, fix authentication errors, and act on unusual sending activity. From there, staying on top of email bounces is straightforward. You should also follow these email security tips to help protect your inbox.