A bounce message tells you an email could not be delivered, or has not been delivered yet. The notice may look technical, but a few details can point you toward the next step.
Maybe you emailed a customer and received an “undeliverable” notice. Or a colleague says your message never arrived. Instead of guessing, look for the delivery result and the numbers beside it.
A bounce is different from an email landing in spam. It means a mail server reported a delivery problem. Here’s how to read the notice calmly and decide what to do.
First, find the useful part
Bounce notices often contain a plain-language explanation and a more detailed technical section. The wording and layout vary between email providers.
Look for labels such as:
- Final-Recipient: The address that the server tried to reach.
- Action: Whether delivery failed, is delayed, or was handled another way.
- Status: A structured code describing the outcome.
- Diagnostic-Code: The server’s explanation, often including a three-digit reply code.
You might also see the name of the reporting server. That can help your email provider identify where the delivery attempt stopped.
These fields may appear in a Delivery Status Notification (DSN), a standard format for reporting email delivery results. The Request for Comments (RFC) 3464 standard describes common fields in these reports.
Don’t worry if your notice uses different labels. The key clues are the recipient, whether the message failed or is delayed, and the complete error text.
Understand the first digit
A server may return a three-digit reply code. The first digit gives you a quick idea of what happened.
- 2 usually means the server accepted the message or completed an action.
- 3 means the server needs more information before continuing.
- 4 means a temporary problem occurred, and another attempt may work.
- 5 means the server rejected the request, and resending unchanged is unlikely to help.
For an everyday reader, the main distinction is between 4 and 5. A 4xx response usually indicates a temporary issue. A 5xx response usually indicates a more lasting rejection.
“Permanent” does not mean nothing can ever be fixed. It means the sender should not keep repeating the same attempt without addressing the cause.
The RFC 5321 standard explains how these Simple Mail Transfer Protocol (SMTP) replies work. You do not need to memorize the standard. Just check whether the first digit is 4 or 5.
Read the enhanced status code
Some bounce notices include a second code with periods, such as 5.1.1 or 4.4.1. This is an enhanced status code. It gives more detail about the general type of failure.
The first number still matters most:
- 4.x.x generally points to a temporary problem.
- 5.x.x generally points to a rejection that needs attention before retrying.
The remaining parts narrow down the issue. The middle number often points to a general category. The final number adds more detail, but its exact meaning can vary.
Here are a few examples you may encounter:
- 5.1.1: The destination mailbox may not exist, or the address may be incorrect.
- 5.2.2: A mailbox condition prevented delivery. A full mailbox is one possible explanation.
- 4.4.1: The sending system could not connect to a destination server. The issue may be temporary.
- 5.7.1: A policy or authorization rule rejected delivery. The server’s full explanation matters.
These are common interpretations, not a complete list. The RFC 3463 enhanced status code standard provides more detail.
Decode a few common phrases
The explanatory text may be more useful than the code alone. Look for direct phrases such as “user unknown,” “domain not found,” or “connection timed out.”
“User unknown” or “recipient address rejected”
Check the address carefully. A mistyped letter, extra character, or outdated contact can send mail to an address that does not exist.
Compare it with a trusted source, such as the person’s website or a previous email thread. Avoid guessing a corrected address based on a display name.
“Domain not found” or “no mail server”
The part of the address after the @ symbol may be wrong, or the domain may have a mail configuration issue. Check the spelling and confirm that you used the recipient’s current address.
If the address looks correct, ask the recipient to check with their email provider or administrator.
“Message delayed” or “still attempting delivery”
This is not necessarily a final failure. The sending system may keep trying for a while before giving up.
Wait for an update before repeatedly sending the same message. If the email is urgent, contact the recipient another way and explain that delivery is delayed.
“Message rejected” or “not authorized”
The receiving server may have blocked the message under one of its rules. The full diagnostic text might mention the message, the sending service, or a policy.
Do not assume that every rejection means your email is spam. If several recipients report similar failures, ask your email provider to review the complete bounce details.
“Mailbox full”
This message means the recipient’s mailbox may not have room to accept more mail. It does not point to a problem with your own mailbox.
You can contact the recipient another way and ask them to check their account. Our guide explains what happens when a mailbox is full.
Check whether it failed or is only delayed
Find the Action field if the notice includes one. It may say “failed” or “delayed.”
A failed result means that delivery attempt has stopped. A delayed result means delivery has not succeeded yet, but the sending system may continue trying.
The reporting mail server is sometimes called a mail transfer agent (MTA). It works behind the scenes, passing messages between email systems. A delay notice can come from one of these systems while it waits for another server to respond.
Also check which recipient the notice names. If you emailed several people, one address may have failed while the others received the message.
A server accepting an email does not prove that a person read it. It only confirms that the server accepted it for further handling.
What to do after reading the notice
Use the error to guide your next move:
- Check the recipient address. Correct any typo before sending again.
- Look for a temporary code. If the response begins with 4, give the system time or contact your provider.
- Read the full explanation. Do not rely on a code without its surrounding text.
- Save the original bounce. Keep the complete notice for support, rather than sending only a cropped screenshot.
- Ask for help if the cause is unclear. Your email provider can review server details that are not visible in your inbox.
If you resend, fix the likely cause first. Sending the same message repeatedly rarely changes a rejected address or server rule.
Treat unexpected bounce notices carefully
Not every message claiming to be a bounce is genuine. If you did not send the email mentioned in the notice, don’t click unfamiliar links or open unexpected attachments.
A bounce may include part or all of the original message. Be thoughtful before forwarding it, especially if it contains customer details or private information.
If you suspect someone used your account, check your Sent folder and contact your email provider through its trusted website or phone number. Never send your password in a reply.
When to ask your provider for help
Contact your email provider or host if the address is correct, failures continue, or the message mentions a server or policy problem you cannot identify.
Share the complete bounce notice, the affected recipient, and approximately when you sent the message. Remove private content that support does not need, but preserve the technical error details.
One delivery failure can be an isolated mistake. A pattern across different recipients may point to a broader configuration or sending issue. Your provider can help distinguish between them.
For background on a different delivery issue, see our guide to why emails land in spam. A bounce means a server reported a delivery problem; spam placement means a message may have reached the recipient’s system.
Keep the notice and take the next sensible step
A bounce message is not just a wall of technical text. Find the recipient, check whether the result says “failed” or “delayed,” and read the full explanation beside the code.
Correct an address when it is wrong. Wait or ask your provider about a temporary server issue. For a policy rejection, get the full details before trying again.
If you need help interpreting a delivery report, visit The CharlesWorks Corner. Save the notice, and let its clues guide your next step.
Focus keyphrase: bounce message
Meta description: Learn how to read a bounce message, distinguish delays from failures, and choose a sensible next step.
Excerpt: A bounce message explains why an email was delayed or rejected. Learn where to find the recipient, action, status, and diagnostic details. This friendly guide explains the difference between temporary and lasting errors, decodes common phrases, and offers practical next steps. Save the full notice and share its details with your email provider if the cause is unclear.
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