Salesforce Email — Mail Non Delivery (NDR) Error Codes Reference

This article provides a reference guide to SMTP NDR (Non Delivery Report) error codes that may be returned when Salesforce emails fail to deliver. The codes are grouped by category for easier navigation.
2xx — Success Codes
These codes indicate the email was accepted or successfully processed by the server.

• 211 — System status message.
• 214 — A help message for a human reader follows.
• 220 — Service ready.
• 221 — Service closing.
• 250 — Requested action taken and completed. The email was delivered successfully.
• 251 — The recipient is not local to the server, but it will accept and forward the message.
• 252 — The recipient cannot be verified, but the server accepts the message and attempts delivery.
• 354 — Start message input and end with CRLF.CRLF. This indicates that the server is ready to accept the message itself.

4xx — Temporary Failure Codes
These codes indicate a temporary problem. The sending server may retry delivery.

• 421 — Service not available; the connection will be closed.
• 422 — The recipient has exceeded their mailbox limit. It could also mean the delivery directory on the Virtual server has exceeded its limit.
• 431 — Not enough disk space on the delivery server. Microsoft may report this NDR as an out-of-memory error.
• 432 — Classic temporary problem: the Administrator has frozen the queue.
• 441 — Intermittent network connection. The server has not yet responded. If it persists, a 5.4.x status code error will also appear.
• 442 — The server started to deliver the message but then the connection was broken.
• 446 — Too many hops. The message is most likely looping.
• 447 — Problem with a timeout. Check receiving server connectors.
• 449 — A DNS problem. Check your smart host setting on the SMTP connector. Verify correct SMTP format and use square brackets around the IP address, for example [197.89.1.4]. This error can also appear if routing groups have been deleted.
• 450 — The requested command failed because the user's mailbox was unavailable.
• 451 — The command has been aborted due to a server error. This is not caused by the sender.
• 452 — The command has been aborted because the server has insufficient system storage.
• 465 — Multi-language situation. The server does not have the correct language code page installed.

5xx — Permanent Failure Codes
These codes indicate a permanent error. The message will not be retried automatically.

• 500 — The server could not recognize the command due to a syntax error.
• 501 — A syntax error was encountered in command arguments.
• 502 — This command is not implemented.
• 503 — The server has encountered a bad sequence of commands.
• 504 — A command parameter is not implemented.
• 510/511 — Problem with the recipient email address. Often seen with contacts in Outlook. Check the recipient address.
• 512 — SMTP 550 Host unknown. An error is triggered when the host name cannot be found. For example, when trying to send an email to bob@nonexistantdomain.com.
• 513 — Problem with contacts. Address field may be empty. Check the address information.
• 514 — Two objects have the same address, which confuses the categorizer.
• 515 — Destination mailbox address invalid.
• 516 — Mailbox may have moved.
• 517 — Problem with sender's mail attribute. Check the properties sheet in Active Directory Users and Computers (ADUC).
• 521 — The message is too large, or it could be a permissions problem. Check the recipient's mailbox.
• 522 — The recipient has exceeded their mailbox limit.
• 523 — Recipient cannot receive messages this large. Server or connector limit exceeded.
• 524 — A distribution list or group is trying to send an email. Check where the expansion server is situated.
• 530 — Problem with the Mail Transfer Agent (MTA). Someone may have edited the registry to disable the MTA/Store driver.
• 531 — Mail system full.
• 532 — System not accepting network messages.
• 533 — Remote server has insufficient disk space to hold the email.
• 534 — Message too big.
• 535 — Multiple Virtual Servers are using the same IP address and port. Email is probably looping.
• 540 — DNS problem. There is no DNS server that can resolve this email address.
• 541 — No answer from host.
• 542 — Bad connection.
• 543 — Routing server failure. No available route.
• 544 — Cannot find the next hop.
• 546 — Looping problem: a contact has the same email address as an Active Directory user. One user is probably using an Alternate Recipient with the same email address as a contact.
• 547 — Delivery time-out. Message is taking too long to be delivered.
• 548 — Bad recipient policy.
• 550 — The requested command failed because the user's mailbox was unavailable (for example, because it was not found, or because the command was rejected for policy reasons). Underlying SMTP 500 error. The sending server tried EHLO, the recipient's server did not understand and returned a 550 or 500 error.
• 551 — The recipient is not local to the server. The server then gives a forwarding address to try.
• 552 — The action was aborted due to exceeded storage allocation. Possibly the disk holding the operating system is full. Or this could be a syntax error if you are running SMTP from a telnet shell.
• 553 — The command was aborted because the mailbox name is invalid. Could also indicate more than 5,000 recipients were specified.
• 554 — The transaction failed.
• 555 — Wrong protocol version.
• 563 — More than 250 attachments.
• 571 — Permissions problem. The sender is not allowed to email this account. An anonymous user may be trying to send mail to a distribution list.
• 572 — Distribution list cannot expand and is unable to deliver its messages.
• 573 — Internal server error, IP address related.
• 574 — Extra security features not supported.
• 575 — Cryptographic failure. Try a plain message with encryption.
• 576 — Certificate problem; encryption level may be too high.
• 577 — Message integrity problem.