SMTP Error Codes
Here is a list of the standard SMTP error codes you will find in most email bounces.
200 Codes
- 211 – System status / system help reply
- 214 – Help message
- 220 – Domain service ready
- 221 – Domain service closing transmission channel
- 250 – Requested mail action completed and OK
- 251 – Not Local User, forward email to forward path
- 252 – Cannot Verify user, will attempt delivery later
- 253 – Pending messages for node started
300 Codes
- 354 – Start mail input; end with .
- 355 – Octet-offset is the transaction offset
400 Codes
- 421 – Domain service not available, closing transmission channel
- 432 – Domain service not available, closing transmission channel
- 450 – Requested mail action not taken: mailbox unavailable. request refused
- 451 – Requested action aborted: local error in processing Request is unable to be processed, try again
- 452 – Requested action not taken: insufficient system storage
- 453 – No mail
- 454 – TLS not available due to temporary reason. Encryption required for requested authentication mechanism
- 458 – Unable to queue messages for node
- 459 – Node not allowed: reason
500 Codes
- 500 – Syntax error, command unrecognized
- 501 – Syntax error in parameters or arguments
- 502 – Command not implemented
- 503 – Bad sequence of commands
- 504 – Command parameter not implemented
- 510 – Check the recipient address
- 512 – Domain can not be found. Unknown host.
- 515 – Destination mailbox address invalid
- 517 – Problem with senders mail attribute, check properties
- 521 – Domain does not accept mail
- 522 – Recipient has exceeded mailbox limit
- 523 – Server limit exceeded. Message too large
- 530 – Access Denied. Authentication required
- 531 – Mail system Full
- 533 – Remote server has insufficient disk space to hold email
- 534 – Authentication mechanism is too weak. Message too big
- 535 – Multiple servers using same IP. Required Authentication
- 538 – Encryption required for requested authentication mechanism
- 540 – Email address has no DNS Server
- 541 – No response from host
- 542 – Bad Connection
- 543 – Routing server failure. No available route
- 546 – Email looping
- 547 – Delivery time-out
- 550 – Requested action not taken: mailbox unavailable
- 551 – User not local; please try forward path
- 552 – Requested mail action aborted: exceeded storage allocation
- 553 – Requested action not taken: mailbox name not allowed
- 554 – Transaction failed
Extended SMTP (ESMTP) standards
Extended SMTP error codes are used in 3 digit combinations. For example, 4.2.1 is a Temporary Error where the receiving email is not accepting messages for now.
The first number is the email message status.
- 2 Successfully sent the email;
- 4 Temporary problem when sending the email. The email server typically will try to send it again till it reaches retry timeout.
- 5 Permanent or Fatal error. This can be caused by a non existent email address, DNS problem, or your email was blocked by the receiving server.
The second 2 numbers pinpoint the exact information bout the error.
Below is a list of the Extended SMTP error codes.
Note! X can be a 4 or a 5 depending on if it is a Temporary or Permanent error.
x.1.x Codes
- X.1.0 – Other address status
- X.1.1 – Bad destination mailbox address
- X.1.2 – Bad destination system address
- X.1.3 – Bad destination mailbox address syntax
- X.1.4 – Destination mailbox address ambiguous
- X.1.5 – Destination mailbox address valid
- X.1.6 – Mailbox has moved
- X.1.7 – Bad sender’s mailbox address syntax
- X.1.8 – Bad sender’s system address
x.2.x Codes
- X.2.0 – Other or undefined mailbox status
- X.2.1 – Mailbox disabled, not accepting messages
- X.2.2 – Mailbox full
- X.2.3 – Message length exceeds administrative limit
- X.2.4 – Mailing list expansion issue
x.3.x Codes
- X.3.0 – Other or undefined mail system status
- X.3.1 – Mail system full
- X.3.2 – System not accepting network messages
- X.3.3 – System not capable of selected features
- X.3.4 – Message too big for system
- X.3.5 – System incorrectly configured
x.4.x Codes
- X.4.0 – Other or undefined network or routing status
- X.4.1 – No answer from host
- X.4.2 – Bad connection
- X.4.3 – Routing server failure
- X.4.4 – Unable to route
- X.4.5 – Network congestion
- X.4.6 – Routing loop detected
- X.4.7 – Delivery time expired
x.5.x Codes
- X.5.0 – Other or undefined protocol status
- X.5.1 – Invalid command
- X.5.2 – Syntax error
- X.5.3 – Too many recipients
- X.5.4 – Invalid command arguments
- X.5.5 – Wrong protocol version
x.6.x Codes
- X.6.0 – Other or undefined media error
- X.6.1 – Media not supported
- X.6.2 – Conversion required and prohibited
- X.6.3 – Conversion required but not supported
- X.6.4 – Conversion with loss performed
- X.6.5 – Conversion failed
x.7.x Codes
- X.7.0 – Other or undefined security status
- X.7.1 – Delivery not authorized, message refused
- X.7.2 – Mailing list expansion prohibited
- X.7.3 – Security conversion required but not possible
- X.7.4 – Security features not supported
- X.7.5 – Cryptographic failure
- X.7.6 – Cryptographic algorithm not supported
- X.7.7 – Message integrity failure
