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When your email cannot be delivered, the outgoing mail server returns with SMTP delivery error codes. These codes are associated with the problem stopping your mail from being sent to the intended recipient. Understanding what the various error messages mean is vital for diagnosing and troubleshooting email account and delivery issues and ensuring effective, consistent communication.
TABLE OF CONTENTS
SMTP Delivery Error Codes Structure
Each SMTP delivery error code consists of three-digit (X.X.X) status codes to communicate between mail servers. Here’s a breakdown of the first-digit categories:
2.X.X
These codes indicate that the requested action (sending) was completed by the server receiving the command but doesn’t guarantee delivery to the recipient’s inbox. It generally means the outgoing server has sent the email to a relay server.
4.X.X
A temporary problem or transient failure, with X.X giving specific information. The sending server may automatically retry sending the email which might be delivered later if the issue resolves itself. Examples include a full mailbox on the recipient’s server or a temporary network issue.
5.X.X
A permanent error where the email is unlikely to be delivered, with X.X giving information about the error code. These need to be fixed manually, like correcting the recipient’s address or fixing authentication issues.
How to Read an SMTP Error Code
To understand an SMTP error code, we’ll use the 550 code as an example:
- The first digit (5) indicates a permanent failure.
- The second digit (5) signifies a mail system issue.
- The third digit (0) provides additional detail within the mail system category.
In this instance, error code 550 signifies that the email could not be delivered as the recipient’s mailbox was unavailable; this may result from an incorrect email address or their mailbox being deactivated.
Common SMTP Error Codes And Their Meanings
Understanding the specific SMTP delivery error codes can help you troubleshoot issues effectively. Here are some common codes and their meanings:
| SMTP Code | Meaning | Explanation | How To Fix |
| 200 | OK | The command was successful. | No action needed; indicates successful processing. |
| 220 | Service Ready | The SMTP server is ready to receive mail. | No action needed; indicates a successful connection. |
| 250 | Request Action Completed | The requested action was completed successfully. | No action is needed; indicates a successful connection. |
| 421 | Service Not Available | The service is not available, and the connection will be closed. | Try again later; this may be a temporary issue. |
| 450 | Requested Action Not Taken | The mailbox is unavailable (e.g., due to a temporary issue). | Wait and try again later; check if the recipient’s mailbox is active. |
| 451 | Requested Action Aborted | The server encountered an error while processing the request. | Check server settings or try again later. |
| 550 | Requested Action Not Taken: Mailbox Unavailable | The recipient’s mailbox is unavailable or does not exist. This is one of the most common SMTP errors. | Verify the recipient’s email address for typos or confirm that their mailbox is active. |
| 551 | User Not Local to Server | The recipient is not local to the server and may need forwarding information. | Check if there’s a forwarding address provided in the message. |
| 552 | Requested Mail Action Aborted: Exceeded Storage Allocation | The recipient’s mailbox has exceeded its storage limit. | Ask the recipient to clear space in their inbox or increase their storage limit. |
| 553 | Requested Action Not Taken: Mailbox Name Invalid | The mailbox name is invalid or improperly formatted. | Verify that you have entered a valid email address format. |
Knowing what the different SMTP delivery error codes are is important for effectively diagnosing why your messages aren’t being received. By understanding the implications of these codes and the appropriate responses, you can facilitate seamless communication and ensure your emails are successfully delivered to their intended recipients without undue delays.
Should you continue to have problems with email delivery after trying to troubleshoot these codes, contact your email service provider for additional assistance and support in addressing any ongoing issues.
Additional Information
Troubleshooting Tips
- Check Address: Double-check for typos in the recipient’s email address.
- Verify DNS Records: These records are essential for mail delivery. Ensure that your domain’s DNS (Domain Name Server) records (MX, SPF, DKIM, DMARC) are configured correctly.
- IP Address Reputation: If your server’s IP address has a bad reputation, like being associated with spamming, it might be blocked by recipient servers. Use online tools to check your IP reputation.
- Contact Recipient Server Admin: If you suspect there is a problem on the recipient’s end, contacting their administrator might be necessary.
