SMTP Error Codes

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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:

More helpful information for each reply code:

mail, misc, postfix, smtp