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Definition
An email bounce back is a delivery failure notification sent when an email cannot reach the recipient. The message usually explains whether the problem is temporary, permanent, caused by the recipient mailbox, or related to the sender’s domain, email server or DNS authentication.
Bounce messages are also called non-delivery reports, delivery status notifications or NDRs. They can look technical, but the key details usually reveal the cause.
Key Takeaways
- Email bounce backs usually fall into two broad groups: hard bounces, which are permanent failures, and soft bounces, which are temporary delivery problems.
- Common causes include mistyped addresses, full mailboxes, blocked attachments, poor sender reputation, authentication failures and incorrect DNS records.
- If business emails bounce regularly, the issue should be investigated because it can affect communication, trust, invoicing, enquiries and email deliverability.
Quick explanation
Why Emails Bounce Back
Bounce types
Hard Bounces vs Soft Bounces
Common Bounce Message Meanings
Bounce wording varies between email providers, but many messages point to similar causes. The exact fix depends on the sender, recipient and domain configuration.
| Bounce message or code | What it often means | What to check |
|---|---|---|
| 550 user unknown or recipient rejected | The recipient address may not exist, may have been disabled, or may be blocked by the receiving server. | Confirm the spelling of the address, check whether the contact has changed email, and avoid repeated sending until confirmed. |
| Mailbox full or quota exceeded | The recipient’s mailbox has no available storage, so the server cannot accept more mail. | Try again later or contact the recipient through another channel if the message is important. |
| SPF, DKIM or DMARC failure | The receiving server could not verify that your email was authorised to send from your domain. | Review DNS authentication records, sending services, domain alignment and any recent email platform changes. |
Troubleshooting Email Bounce Backs
Start with the bounce message itself. It usually contains the failed recipient, the server that rejected the email and a status code or explanation.
Only one recipient bounces
Likely cause
The recipient address may be wrong, inactive, full or rejecting messages because of a local policy.
Solution
Check the spelling, remove extra spaces, confirm the address with the recipient and try again only after the address is verified.
Many recipients bounce at once
Likely cause
Your email platform, DNS records, domain authentication or sending reputation may have changed or failed.
Solution
Check SPF, DKIM, DMARC, MX records, recent DNS changes, email provider alerts and whether a third-party sending tool is properly authorised.
Website form emails bounce or never arrive
Likely cause
The website may be sending from an unauthorised address, the recipient mailbox may reject the message, or domain authentication may be incomplete.
Solution
Review the form sender address, mail routing, DNS authentication and website hosting configuration. A form should send in a way that aligns with the domain’s email policy.
Do Not Ignore Repeated Bounce Backs
DNS and authentication
How DNS Records Affect Email Delivery
Email Bounce Back Terms
These terms often appear in bounce messages and email delivery diagnostics.
- NDR
- A non-delivery report is the message sent back to the sender when an email cannot be delivered.
- SMTP status code
- A technical code that explains the delivery result. Codes beginning with 4 usually indicate temporary problems, while codes beginning with 5 usually indicate permanent failures.
- Sender reputation
- A trust signal used by email systems. It can be affected by bounce rates, spam complaints, sending patterns and domain authentication.
Diagnosis process
How to Read a Bounce Message
Bounce messages can be long, but you can usually diagnose the issue by looking at three parts.
-
Find the failed recipient address
Check which email address bounced. If only one address is affected, the issue is often with that address or recipient mailbox.
-
Look for the status code
A 5xx code usually indicates a permanent failure, while a 4xx code usually indicates a temporary issue. The wording beside the code often gives the clearest clue.
-
Check whether the message mentions authentication
References to SPF, DKIM, DMARC, policy rejection or unauthorised sender suggest a domain or email platform configuration issue.
Common Mistakes That Make Bounce Backs Worse
Many email problems are made worse by guessing at the fix. A careful review is safer than changing records at random.
Keeping invalid addresses in a contact list
Do this instead
Remove or verify addresses that hard bounce. Repeatedly sending to invalid addresses can harm sender reputation.
Changing DNS records without documenting the current setup
Do this instead
Record existing MX, SPF, DKIM and DMARC settings before making changes. This helps you reverse or compare changes if delivery breaks.
Assuming email delivery and inbox placement are the same
Do this instead
A delivered email can still land in spam. Authentication helps, but content, reputation, recipient behaviour and provider rules also influence placement.
Email Bounce Review Checklist
Use this checklist when bounce backs become frequent, affect multiple people, or start after a platform change.
-
Confirm the bounce pattern
Check whether the issue affects one recipient, one sender, one domain, website forms, or the whole business.
-
Review email authentication
Check SPF, DKIM and DMARC records, especially if you use Microsoft 365, a website form, CRM, invoicing tool or marketing platform.
-
Check recent changes
Look for DNS changes, domain transfers, hosting migrations, mailbox changes, new sending tools or security policy updates.
When to get help
Can You Fix Email Bounce Backs Yourself?
Our approach
How We Approach Business Email Deliverability
Email Bounce Back FAQs
These answers cover common questions businesses ask when emails start bouncing.
Does a bounced email mean my email account is broken?
Can SPF, DKIM and DMARC stop all bounce backs?
Why do emails from my website form bounce?
Need Help Diagnosing Email Bounce Backs?
If business emails are bouncing, landing in spam or failing after a domain, hosting or Microsoft 365 change, we can review the technical setup and explain what needs attention.