Email hard bounces: what they are and how to manage them

Introduction

Email marketing success depends on getting your emails delivered to your subscribers’ inboxes. However, this process isn’t always smooth. One of the biggest challenges email marketers face is dealing with email hard bounces—permanent email delivery failures that can harm your sender reputation and reduce campaign effectiveness.

Understanding what email hard bounces are, why they happen, and how to manage them can help keep your email list clean and ensure your messages reach the right audience. In this article, we’ll explain the causes of hard bounces, share best practices for prevention, and show how Xendy automates hard bounce management to improve deliverability.

What is an email hard bounce?

An email hard bounce occurs when an email cannot be delivered due to a permanent failure. This means the recipient’s server has rejected the email because the email address is either invalid, doesn’t exist, or has been blocked. Unlike soft bounces, which are temporary and can be retried, hard bounces require immediate action, such as removing the email address from your list to maintain a good sender reputation.

Why do hard bounces matter?

Hard bounces are a critical factor in email marketing because they can:

• Damage your sender reputation: Consistently high hard bounce rates signal to email service providers that you’re sending emails to invalid or inactive addresses, potentially leading to blacklisting.
• Lower email deliverability: Providers may filter future campaigns as spam if your sender score drops.
• Skew campaign metrics: Hard bounces affect your open and click-through rates by inflating delivery numbers with unreachable addresses.

What you’ll learn in this article

We’ll cover the following topics:

• How hard bounces happen: An overview of the delivery process and where hard bounces occur.
• Common causes of hard bounces: Detailed explanations of why email addresses fail permanently.
• How to prevent hard bounces: Practical tips to reduce email delivery failures.
• How Xendy manages hard bounces: Automatic detection, removal, and real-time reporting to keep your campaigns running smoothly.

What is an email hard bounce?

An email hard bounce is a permanent email delivery failure, meaning the email you tried to send could not reach the recipient’s inbox, and retrying won’t solve the issue. When a hard bounce occurs, the email server sends back a bounce notification, also known as a non-delivery report (NDR), indicating that delivery has failed permanently.

How email hard bounces work

Here’s what happens during the email delivery process and when a hard bounce is triggered:

1. Email sent: The sender’s email server sends the email to the recipient’s mail server.
2. Email verification: The recipient’s mail server verifies:
   • The email address’s validity.
   • The domain name’s existence.
   • The sender’s authentication records (SPF, DKIM, DMARC).
3. Permanent rejection: If the email address is invalid, blocked, or the domain doesn’t exist, the recipient’s server rejects the email permanently and sends back a bounce notification.
4. Bounce notification: The sender’s email platform logs the failure and provides details such as the reason for the bounce and an error code.

What does a bounce notification include?

A typical bounce notification includes:

• Error code: A numeric code identifying the type of delivery failure.
• Reason for the bounce: An explanation such as “invalid recipient” or “non-existent domain.”
• Server response: A more detailed technical message from the recipient’s mail server.

Key differences: hard bounce vs. soft bounce

Category	Hard bounce	Soft bounce
Definition	Permanent delivery failure	Temporary delivery issue
Causes	Invalid email, non-existent domain	Full inbox, server downtime
Retry attempts	No retries after detection	Automatically retried by server
Action needed	Remove address from list	Monitor and retry later

Why hard bounces matter

Hard bounces are a warning sign that your email list may contain outdated or fake addresses. Ignoring hard bounces can cause serious issues, such as:

• Damaging your sender reputation: Too many hard bounces lower your email sending score, causing future emails to be filtered as spam.
• Triggering blacklists: Email providers may blocklist your domain or IP if high hard bounce rates persist.
• Wasting marketing efforts: Sending emails to invalid addresses wastes time, money, and resources while skewing email campaign metrics.

How email hard bounces happen

Email hard bounces occur when an email cannot be delivered due to a permanent failure. This means the recipient’s email server rejects the message without retrying, and the issue cannot be resolved automatically. Understanding where hard bounces happen in the email delivery process helps you take corrective action to avoid similar issues in the future.

The email delivery process

Here’s how the email delivery process works and where hard bounces can occur:

1. Email composition: The sender creates the email and initiates sending through an email marketing platform like Xendy.

2. Sender’s server processing: The sender’s email service routes the email through a mail transfer agent (MTA).

3. Email transmission: The email is transmitted across the internet to the recipient’s mail server.

4. Recipient server verification:

   • The recipient’s email server checks if the email address exists.
   • It verifies whether the sender’s domain and IP are properly authenticated (SPF, DKIM, DMARC).
   • It assesses whether the email content passes spam filters.

5. Delivery success or hard bounce:

   • Success: If all checks pass, the email is delivered to the inbox.
   • Hard bounce: If the address is invalid, the domain doesn’t exist, or the sender is blocked, the email is rejected, resulting in a hard bounce.

When hard bounces are triggered

Here are the most common situations where hard bounces occur:

Invalid email address

• What happens: The email address is incorrectly formatted or doesn’t exist.
• Example: Sending an email to “johndoe@example.cm” instead of “johndoe@example.com.”

Non-existent domain

• What happens: The domain linked to the email address no longer exists or is misspelled.
• Example: “@companyxyz.com” is typed instead of “@company.com.”

Recipient blocked sender

• What happens: The recipient’s email server has blocked the sender’s domain due to blacklisting, spam complaints, or IP reputation issues.

DNS misconfiguration

• What happens: If the domain’s DNS records are not correctly configured, the recipient’s server will reject the email due to failed authentication.

Email server blacklisting

• What happens: The sender’s IP address or domain has been added to a spam blacklist, automatically causing email rejection.

Blocked by spam filters

• What happens: If the recipient’s spam filter flags the sender as suspicious, the email will be rejected, especially if authentication records are missing.

How Xendy manages hard bounces automatically

Hard bounce cause	How Xendy handles it	Action taken
Invalid email address	Automatically removed from the list	No retries, address deactivated
Non-existent domain	Deactivated and flagged for review	Email address removed
Blocked sender (blacklisting)	Domain flagged for blacklist checks	Campaign paused for review
DNS misconfiguration	Notification sent to the sender	Requires manual correction
Spam filter rejection	Email flagged and logged	User notified for spam score analysis
Blacklisted server/ip	Server flagged for review	Requires administrative action

Common causes of email hard bounces

Email hard bounces occur due to permanent issues that prevent email delivery. These issues typically stem from invalid email addresses, domain problems, or server-related rejections. Understanding these causes helps marketers proactively manage their email lists and reduce bounce rates.

Common causes of email hard bounces

Here are the most frequent reasons behind email hard bounces, along with examples and potential solutions:

Invalid email address

What happens:

• The email address doesn’t exist, is misspelled, or was entered incorrectly during signup.

Example:

• Typing “johndo@exmple.com” instead of “johndoe@example.com.”

Solution:

• Use email verification tools.
• Implement a double opt-in process to confirm email validity.

Non-existent domain

What happens:

• The domain linked to the email address doesn’t exist or has been deactivated.

Example:

• Sending an email to “user@nonexistentdomain.xyz.”

Solution:

• Verify domains before sending campaigns.
• Regularly clean email lists to remove invalid domains.

Blocked sender (blacklisted ip or domain)

What happens:

• The sender’s domain or IP address is blacklisted due to spam complaints, suspicious activity, or low engagement rates.

Example:

• The sending domain “yourbrand.com” is blacklisted for sending spam-like emails.

Solution:

• Monitor email sending reputation using tools like SenderScore or MXToolbox.
• Follow anti-spam best practices and authenticate your domain with SPF, DKIM, and DMARC records.

Incorrect email format

What happens:

• The email address is improperly formatted, causing it to be rejected by the recipient’s email server.

Example:

• Missing the “@” symbol, such as “userexample.com” instead of “user@example.com.”

Solution:

• Validate email addresses during form submissions.
• Use input validation scripts on signup forms.

DNS misconfiguration

What happens:

• The sender’s email domain has incorrect DNS records, failing essential email authentication checks like SPF, DKIM, and DMARC.

Example:

• Missing DNS entries cause emails to be rejected by recipient servers.

Solution:

• Set up and regularly update SPF, DKIM, and DMARC records.
• Use DNS management tools or consult an IT professional.

Blocked by spam filters

What happens:

• Emails are blocked because the content triggers spam filters, often due to suspicious subject lines, excessive links, or spam-like content.

Example:

• An email with the subject line “WIN FREE MONEY NOW!!” gets flagged as spam.

Solution:

• Avoid spam trigger words and excessive links.
• Use a reputable email marketing platform with spam score analysis, like Xendy.

Recipient’s email server policy

What happens:

• The recipient’s email server rejects the email due to strict security or content policies.

Example:

• A business email server rejecting all external email attachments for security reasons.

Solution:

• Use a professional sending domain.
• Follow email sending guidelines and avoid suspicious attachments.

Summary of common causes of email hard bounces

Cause	Description	Solution
Invalid email address	Email address misspelled or fake	Use email validation tools
Non-existent domain	Domain doesn’t exist or inactive	Verify domains before sending
Blocked sender (blacklist)	Domain/ip blocked for spam activity	Monitor sender reputation
Incorrect email format	Invalid structure or missing symbols	Validate email input fields
DNS misconfiguration	DNS records missing or incorrect	Set up SPF, DKIM, and DMARC
Blocked by spam filters	Spam-like content in email	Avoid spam trigger words
Recipient email policy	Server blocks unknown senders	Use a professional sending domain

How to prevent email hard bounces

Preventing email hard bounces is essential for maintaining a healthy email list, protecting your sender reputation, and improving the success of your email marketing campaigns. Here are the most effective strategies for reducing email hard bounces:

Maintain a clean email list

Why it matters:

Sending emails to invalid or outdated addresses increases your bounce rate and damages your sender reputation.

Best practices:

• Regularly update your list: Remove inactive or unresponsive subscribers every 3-6 months.
• Use email verification tools: Check the validity of email addresses during signups.
• Automate list cleaning: Use an email marketing platform like Xendy, which automatically removes invalid addresses after a hard bounce.

Use a double opt-in process

Why it matters:

Double opt-in ensures only valid email addresses are added to your list, reducing fake signups and data entry mistakes.

How it works:

1. A user submits their email on your signup form.
2. They receive a confirmation email with a verification link.
3. Clicking the link confirms their subscription and validates the email address.

Tip: Enable double opt-in in your email platform’s settings for automated address validation.

Authenticate your sending domain

Why it matters:

Authentication records build trust with email service providers and reduce the risk of being flagged as spam or blocked.

Best practices:

• Set up SPF (sender policy framework): Verifies that your email is sent from a legitimate source.
• Implement DKIM (domainkeys identified mail): Ensures your email content hasn’t been altered during delivery.
• Use DMARC (domain-based message authentication): Protects against spoofing and phishing attempts by verifying email authenticity.

Tip: Xendy provides a step-by-step guide for setting up email authentication records.

Avoid spam-like content

Why it matters:

Emails that look like spam are more likely to be blocked or rejected by recipient servers.

Best practices:

• Use a professional sender name: Avoid sending emails from generic addresses like “no-reply@domain.com.”
• Avoid spam trigger words: Steer clear of words like “FREE,” “WIN NOW,” “GUARANTEED,” or “ACT FAST!”
• Limit links and attachments: Keep the number of links and file attachments to a minimum.
• Include a clear call-to-action (CTA): Ensure the email has a clear and relevant purpose.

Tip: Use Xendy’s spam checker tool to scan your email content before sending.

Verify email addresses during signup

Why it matters:

Validating email addresses at the point of signup prevents incorrect or fake addresses from entering your list.

Best practices:

• Add real-time validation: Use validation scripts on your signup forms.
• Confirm email format: Ensure correct formatting before adding emails to your list.

Monitor your sender reputation

Why it matters:

Your sender reputation determines whether your emails are delivered or marked as spam by recipient servers.

Best practices:

• Check blacklists regularly: Use tools like MXToolbox or SenderScore.
• Monitor campaign metrics: Track bounce rates, open rates, and click-through rates to identify issues early.
• Engage with active subscribers: Focus on sending personalized, relevant content to engaged users.

Tip: Xendy tracks sender reputation and bounce metrics in real-time, helping you maintain good standing with email service providers.

Monitor bounce reports and take action

Why it matters:

Regularly reviewing your campaign reports helps identify problem areas and take corrective action.

Best practices:

• Track hard bounces by campaign: Check bounce rates after every email campaign.
• Identify recurrent issues: Look for patterns such as repeated bounces from specific domains.
• Remove hard-bounced addresses: Automatically remove emails flagged as hard bounces to prevent future delivery issues.

Tip: Xendy provides detailed campaign reports with bounce reasons, error codes, and actionable insights.

Summary of hard bounce prevention tips

Action	Why it matters	How to do it
Maintain a clean email list	Reduces invalid email addresses	Use email verification tools
Use double opt-in	Prevents fake email signups	Enable in your email platform
Authenticate your domain	Builds trust with servers	Set up SPF, DKIM, and DMARC
Avoid spam-like content	Prevents spam filtering	Use Xendy’s spam checker tool
Verify emails during signup	Avoids incorrect addresses	Use real-time validation scripts
Monitor sender reputation	Prevents blacklisting	Track sender score tools
Use a trusted esp	Ensures high deliverability	Choose reputable email platforms
Monitor campaign reports	Identifies recurring issues	Check email performance metrics

How Xendy manages email hard bounces

Xendy’s email marketing platform automatically detects, manages, and reduces email hard bounces, helping marketers maintain high deliverability and protect their sender reputation. With built-in automation, bounce reporting, and proactive list management, Xendy simplifies the process of managing hard bounces so you can focus on crafting better campaigns.

How Xendy handles email hard bounces

Here’s how Xendy deals with different hard bounce causes and automates key actions:

Invalid email address

What happens:

• The recipient’s email address doesn’t exist or is incorrectly formatted.

Xendy’s action:

• Automatic removal: Xendy automatically deactivates and removes invalid addresses after a hard bounce is detected.

Non-existent domain

What happens:

• The email domain associated with the recipient’s email address no longer exists or is inactive.

Xendy’s action:

• Email blocked: The address is permanently blocked and removed from future campaigns.
• Bounce logging: Xendy records the failed attempt in the campaign report for review.

Blocked sender (blacklisted ip or domain)

What happens:

• The sender’s IP address or domain has been blacklisted due to spam complaints or suspicious activity.

Xendy’s action:

• Domain flagged: Xendy flags the domain for review and pauses all campaigns to avoid further delivery issues.
• User alert: A real-time alert is sent to the sender with instructions on how to fix the issue.

DNS misconfiguration (authentication failures)

What happens:

• The sender’s domain lacks proper DNS authentication records like SPF, DKIM, or DMARC, causing email rejection.

Xendy’s action:

• Authentication error detected: Xendy detects missing DNS records and sends a configuration alert to the sender.
• Campaign halted: Campaigns are paused automatically until the issue is fixed.

Blocked by spam filters

What happens:

• The email is flagged by the recipient’s spam filters due to suspicious content, excessive links, or missing authentication records.

Xendy’s action:

• Content flagged: Xendy runs a spam analysis on email content before sending.
• Recommendation issued: The platform suggests improvements such as removing spam-triggering keywords, fixing email formatting, or enabling domain authentication.

Incorrect email format

What happens:

• The email address is formatted incorrectly, missing elements like the “@” symbol or the domain name.

Xendy’s action:

• Data validation: Xendy rejects invalid email addresses at signup or during list import using email verification tools.
• Error notification: An import error message is sent to the sender with a list of invalid addresses.

Automated bounce management features in Xendy

Xendy offers a range of automated features designed to manage and reduce email hard bounces effectively:

Automatic email list cleaning

• Hard bounce removal: Xendy automatically removes hard-bounced email addresses from future campaigns, keeping your email list clean.

Bounce notification alerts

• Real-time alerts: Xendy sends instant notifications with detailed bounce reasons and corrective actions.

Detailed campaign reports

• Bounce analytics: Campaign reports provide insights into bounce rates, error codes, and bounce reasons, helping marketers identify and fix recurring issues.

Spam score checker

• Content analysis: Xendy’s spam checker tool scans your email content for potential spam triggers before sending, reducing the chances of being blocked by spam filters.

Domain authentication assistance

• Authentication setup guide: Xendy provides a step-by-step guide for setting up SPF, DKIM, and DMARC records to improve email authentication and reduce bounce risks.

Domain blacklist monitoring

• Blacklist monitoring: Xendy monitors IP blacklists and notifies users if their sending domain is flagged, enabling timely corrective action.

How Xendy improves email deliverability

By automating bounce management and reducing hard bounce rates, Xendy helps businesses:

• Protect sender reputation: By preventing emails from being sent to invalid addresses.
• Maintain list quality: With auto-removal of hard-bounced emails.
• Boost campaign success: With cleaner email lists and improved deliverability.
• Save time: By automating repetitive bounce management tasks.

Frequently asked questions