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SMTP Response Codes

RFC 5321 / RFC 346346 codes

Email server codes from 220 to 554

Showing 46 of 46 errors

Code	Message	Severity	Tier
211	System status, or system help reply	INFO	Critical	→
214	Help message	INFO	Critical	→
220	<domain> Service ready	INFO	Critical	→
221	<domain> Service closing transmission channel	INFO	Critical	→
250	Requested mail action okay, completed	INFO	Critical	→
251	User not local; will forward to <forward-path>	INFO	Critical	→
252	Cannot VRFY user, but will accept message and attempt delivery	INFO	Critical	→
334	Server challenge	INFO	Notable	→
354	Start mail input; end with <CRLF>.<CRLF>	INFO	Critical	→
421	Service not available, closing transmission channel	WARN	Notable	→
450	Requested mail action not taken: mailbox unavailable	WARN	Notable	→
451	Requested action aborted: local error in processing	WARN	Notable	→
452	Requested action not taken: insufficient system storage	WARN	Notable	→
455	Server unable to accommodate parameters	WARN	Notable	→
500	Syntax error, command unrecognized	ERROR	Common	→
501	Syntax error in parameters or arguments	ERROR	Common	→
502	Command not implemented	ERROR	Common	→
503	Bad sequence of commands	ERROR	Common	→
504	Command parameter not implemented	ERROR	Common	→
535	Authentication credentials invalid	ERROR	Notable	→
550	Requested action not taken: mailbox unavailable	ERROR	Common	→
551	User not local; please try <forward-path>	ERROR	Common	→
552	Requested mail action aborted: exceeded storage allocation	ERROR	Common	→
553	Requested action not taken: mailbox name not allowed	ERROR	Common	→
554	Transaction failed	ERROR	Common	→
555	MAIL FROM/RCPT TO parameters not recognized or not implemented	ERROR	Common	→
5.1.1	Bad destination mailbox address — mailbox does not exist	ERROR	Notable	→
5.1.2	Bad destination system address — domain does not exist or has no MX record	ERROR	Notable	→
5.1.3	Bad destination mailbox address syntax — malformed email address	ERROR	Notable	→
5.1.6	Mailbox has moved — no forwarding address available	ERROR	Notable	→
5.2.1	Mailbox disabled — not accepting messages	ERROR	Notable	→
5.2.2	Mailbox full — over storage quota	ERROR	Notable	→
5.2.3	Message length exceeds administrative limit	ERROR	Notable	→
5.3.4	Message too big for system	ERROR	Notable	→
5.4.1	No answer from host — connection timeout	ERROR	Notable	→
4.4.2	Bad connection — transient network problem	WARNING	Notable	→
4.4.7	Delivery time expired — message queued too long without delivery	WARNING	Notable	→
5.4.4	Unable to route — no route to destination	ERROR	Notable	→
5.5.1	Invalid command	ERROR	Common	→
5.5.2	Syntax error	ERROR	Common	→
5.5.3	Too many recipients	ERROR	Notable	→
5.7.1	Delivery not authorized — relaying denied or policy rejection (SPF/DMARC)	ERROR	Common	→
5.7.8	Authentication credentials invalid — SMTP AUTH failure	ERROR	Common	→
5.7.25	Reverse DNS validation failed — PTR record missing or mismatched	ERROR	Common	→
5.7.26	Multiple authentication checks failed — SPF and DKIM both fail	ERROR	Common	→
2.0.0	Other or undefined status — generic success	INFO	Critical	→