The following table displays the SMTP error or response codes. This is sometimes written like “512” and sometimes written like “5.1.2”. These two ways of writing the code are synonymous.
Code | Meaning |
---|---|
211 | Indicates the system status or system help reply |
214 | Help message |
220 | Service ready |
221 | Service closing transmission channel |
250 | Requested mail action ok, completed |
251 | User not local |
252 | Cannot VRFY user, but will still accept message and attempt to deliver |
354 | Start mail input |
421 | Service not available, closing transmission channel |
450 | Requested mail action not taken: mailbox unavailable |
451 | Requested mail action aborted: local error |
452 | Requested action not taken: insufficient storage |
500 | Syntax error - command not recognized |
501 | Syntax error in command, parameters, or message fields |
502 | Command not implemented |
503 | Bad sequence of commands or authentication required to use command |
504 | Command parameter not implemented |
510 | Bad email address |
511 | Bad email address |
512 | Unable to resolve recipient domain (DNS error) |
513 | Address type is incorrect |
523 | Message too large for recipient’s mailbox |
530 | Authentication required or server blacklisted by recipient or no such recipient mailbox |
541 | Recipient address rejected - blocked by antispam, intrusion prevention, or mail filtering |
550 | Recipient mailbox unavailable |
551 | Invalid recipient address; relay denied |
552 | Size of incoming message exceeds storage limit |
553 | Mailbox name invalid or authentication required or reverse DNS lookup failure |
554 | Transaction failed - address doesn’t exist or rejected due to blacklist |
Further reading
Official documentation:
https://www.iana.org/assignments/smtp-enhanced-status-codes/smtp-enhanced-status-codes.xhtml
More helpful information for each reply code:
http://www.answersthatwork.com/Download_Area/ATW_Library/Networking/Network__3-SMTP_Server_Status_Codes_and_SMTP_Error_Codes.pdf
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