Email Delivery
How to Read an Email Bounce Message
Quick Answer
A bounce message contains a status code and a text explanation from the receiving server describing exactly why a message was rejected. Reading the full text, not just the subject line, usually reveals the actual cause.
Bounce messages look intimidating because they include technical headers, but the useful information is often a single plain-language line explaining the rejection reason.
Common Causes
- Skimming only the bounce subject line and missing the detailed reason in the body.
- Not distinguishing between a permanent failure (5xx code) and a temporary one (4xx code).
- Assuming every bounce means the same thing, when causes vary widely.
Safe Troubleshooting Steps
- Open the full bounce message, not just the notification subject line.
- Look for a status code (like 550, 421, 552) and the explanation text near it.
- Search for that specific code and message text to understand what it typically indicates.
- Match the reason to a category: authentication failure, full mailbox, blocked sender, or unknown user.
What to Verify
- You have the full bounce text, not a summary.
- You can identify whether the failure is permanent or temporary based on the code.
When Professional Help May Be Useful
If a bounce message references something unfamiliar (like a specific authentication failure or reputation block), it can help to have it reviewed by someone who deals with these regularly rather than guessing at the meaning.