A bounce message (also called a "Mail delivery failed" or "Undeliverable" email) is an automatic reply telling you that a message you sent didn't arrive. It looks technical, but it almost always tells you exactly what went wrong. This guide shows you how to read a bounce message and fix the most common email errors.
How to read a bounce message
Bounces from the Instant Access Internet Services server usually start with "This message was created automatically by mail delivery software". Look for three things:
- The recipient address it failed for. Check it for typos first -- this is the cause more often than anything else.
- Whether it's permanent. "This is a permanent error" or a code starting with 5 (such as 550) means the message will not be retried. A code starting with 4, or wording like "delayed" or "will keep trying", is temporary -- the server is still retrying and you may not need to do anything.
- The error line from the receiving server, often shown after the address, such as
550 5.1.1 User unknown. The three-digit code plus the words after it are the real explanation.
Your original message is usually attached or quoted at the bottom so you can resend it after fixing the problem.
Common bounce errors and what they mean
| Error text (examples) | What it means | What to do |
|---|---|---|
| 550 5.1.1 User unknown, No such user, Recipient address rejected, mailbox unavailable | The address doesn't exist at the other end. | Check the spelling. Confirm the address with the person by phone or another channel. |
| 552 / 452 Mailbox full, Quota exceeded, over quota | The recipient's mailbox is out of space. | Nothing you can fix -- tell the person. If it's one of your mailboxes, see How to Fix "Mailbox Full" Errors. |
| 550 5.7.1 / 554 Message rejected as spam, Blocked, Listed on a blocklist | The receiving server thinks the message or the sending server looks like spam. | Remove spammy wording, large attachments and link shorteners. Make sure SPF and DKIM are set up (see Why Your Emails Go to Spam (and How to Fix It)). Send the full bounce to us in a ticket if it names a blocklist. |
| SPF fail, DMARC policy, 5.7.26 Unauthenticated email, sender not authorized | Your domain's email authentication didn't pass. | Fix SPF, DKIM and DMARC in cPanel (see How to Set Up SPF and DKIM with Email Deliverability and How to Add a DMARC Record to Your Domain). |
| Host or domain name not found, Name service error, no MX record | The recipient's domain doesn't exist or has broken DNS. | Check the part after the @ for typos (gmial.com, yahooo.com). |
| Retry time not reached / retry timeout exceeded, Connection timed out | Our server tried for several days but couldn't reach the other server. | The recipient's mail server is down or blocking us. Try again later or contact them another way. |
| Message size exceeds limit, 552 message too large | The attachment is bigger than the receiving server accepts. | Send a smaller file, or share it with a download link instead. |
| Relay not permitted, relay access denied, authentication required | The server refused to send because you weren't logged in to it. | Turn on SMTP authentication in your mail app (see How to Fix "Cannot Send Email" (SMTP Authentication Errors)). |
| Too many recipients, rate limit, sending limit exceeded | You sent to too many people at once or too quickly. | Send in smaller batches. For newsletters, use a mailing service. |
How to see more detail in cPanel
If the bounce is unclear, or you never received a bounce but the person says the email didn't arrive, use Email > Track Delivery in cPanel. It shows whether our server accepted, delivered, deferred or rejected each message, with the full reason (see How to Find a Missing Email with Track Delivery).
Common questions
I got a bounce for an email I never sent
This is called backscatter. Spammers often forge real addresses in the "From" line, and the bounces come back to you. If the original message in the bounce isn't something you wrote and it wasn't sent from our server (Track Delivery won't show it), you can safely delete it. Setting up SPF, DKIM and DMARC makes forging your domain much harder (see How to Add a DMARC Record to Your Domain). If you think your account really is sending spam, change your email passwords right away (see How to Change an Email Account Password in cPanel) and open a ticket.
Why did it bounce from one person but not others?
Each receiving server has its own rules. One company might block a certain attachment type or have a full mailbox while everyone else gets your email fine. The error line tells you which rule you hit.
People say their emails to me bounce
Ask them to send you the bounce. "Mailbox full" means your quota needs raising or clearing (see How to Free Up Mailbox Space with Email Disk Usage). "User unknown" means the address doesn't exist here -- check it in Email Accounts or create a forwarder (see How to Create an Email Forwarder in cPanel). If you recently moved your domain, DNS may still be updating (see DNS Propagation: Why Domain Changes Take Time and How to Check).
Related guides
- How to Find a Missing Email with Track Delivery
- Why Your Emails Go to Spam (and How to Fix It)
- How to Fix "Mailbox Full" Errors
- How to Fix "Cannot Send Email" (SMTP Authentication Errors)
- How to Set Up SPF and DKIM with Email Deliverability
Still stuck? Open a support ticket and the Instant Access Internet Services team will help.
