A bounce message tells you why an email did not arrive. The code and the words in the message point to the cause: a wrong address, a full mailbox, a blocked message or a DNS problem.
Overview
When a mail server cannot deliver an email, it sends back a bounce message. Reading the text in it is the fastest way to find the fix.
Why it happens
- The address has a typo or does not exist (user unknown).
- The mailbox is full.
- The receiving server judged the message to be spam or the sender's domain failed its checks.
- The domain's MX records are missing or wrong.
What it means
Bounces are normal when addresses are wrong. If real addresses bounce, look at the message text and the sender's domain settings.
How to fix it
- "User unknown" or "no such user": check the spelling of the address.
- "Mailbox full" or "over quota": the receiver must free space, or free space in your mailbox.
- "Blocked", "spam" or "policy": see emails going to spam.
- "Domain not found" or no mail at all: check your MX records: keep email working.
- Send the full bounce text in a ticket if you are not sure.
Still need help? Get support
Open a support ticket
A ticket is the best way to get this fixed: it keeps your details, and we reply in the ticket.
Prefer to talk? Call 0758 309 999 (fastest line). If that line is busy, call 0753 930 000 (longer wait).
Related articles
- Emails Going to Spam or Not Reaching Gmail: How to Fix It
- Mailbox Full or Over Quota: How to Free Space or Upgrade
- Business Email Help: Start Here (info@yourdomain, Setup, Problems)
- Email Not Sending or Receiving: Step-by-Step Diagnostic Guide
- Read the full guide: why business emails go to spam in Gmail
Frequently asked questions
What does 550 mean?
It is a permanent failure. The server refused the message, for example an unknown address or a blocked sender.
What does 554 mean?
Usually the message was rejected as spam or by a security policy.
Written by Jumbe Nylon, Founder & CTO, SakuraHost. Updated October 2026.