---
title: "Common email error messages"
url: "https://inleed.com/helpcenter/email-error-messages"
language: "en"
updated: "2026-11-06"
category: "Email"
type: "referens"
---

# Common email error messages

When email bounces, a bounce message comes back with an error code. Here is what the most common codes mean and what to do.

## Common error messages

| Error message | What it means and what to do |
| --- | --- |
| 550 User unknown | The address doesn’t exist at the recipient. Check the spelling. |
| 552 Mailbox full | The recipient’s mailbox is full. Try again later. |
| 535 Authentication failed | Wrong username or password in your email app. Use the full email address as the username. |
| 550 User account has sent too many emails | The sending limit has been reached, and sending is stopped for a while. |
| 554 eller 550 5.7.1, S3150 | The recipient, often Microsoft, has blocked the server’s IP address. Contact support. Once the block is lifted, send the email again. |
| 550 5.7.26, SPF fail, DMARC fail | The email lacks the right SPF, DKIM or DMARC. |
| Message size exceeds | The attachment is too large. Send a link instead. |

## Good to know

- If you get an authentication error, check the settings in your email app.  
  [Email client settings](https://inleed.com/helpcenter/email-client-settings)
- If it is about SPF, DKIM or DMARC, go through the guide on them.  
  [Set up SPF, DKIM and DMARC for your domain](https://inleed.com/helpcenter/set-up-spf-dkim-dmarc)
- If you need help, send the whole bounce message to [support](mailto:support@inleed.se).

## Related guides

- [I can’t send email](https://inleed.com/helpcenter/cant-send-email)
- [Set up SPF, DKIM and DMARC for your domain](https://inleed.com/helpcenter/set-up-spf-dkim-dmarc)
- [Email client settings](https://inleed.com/helpcenter/email-client-settings)
- [Email in the new Outlook for Windows](https://inleed.com/helpcenter/email-new-outlook-windows)