This is a list of Simple Mail Transfer Protocol (SMTP) response status codes. Status codes are issued by a server in response to a client's request made to the server.
Unless otherwise stated, all status codes described here is part of the current SMTP standard, RFC 5321. The message phrases shown are typical, but any human-readable alternative may be provided.
A "Basic Status Code" SMTP reply consists of a three digit number (transmitted as three numeric characters) followed by some text. The number is for use by automata (e.g., email clients) to determine what state to enter next; the text ("Text Part") is for the human user.
The first digit denotes whether the response is good, bad, or incomplete:
The second digit encodes responses in specific categories:
The Basic Status Codes have been in SMTP from the beginning, with RFC 821 in 1982, but were extended rather extensively, and haphazardly so that by 2003 RFC 3463 rather grumpily noted that: "SMTP suffers some scars from history, most notably the unfortunate damage to the reply code extension mechanism by uncontrolled use."
RFC 3463 defines a separate series of enhanced mail system status codes which is intended to be better structured, consisting of three numerical fields separated by ".", as follows:
class "." subject "." detail class = "2" / "4" / "5" subject = 1 to 3 digits detail = 1 to 3 digits
The classes are defined as follows:
In general the class identifier MUST match the first digit of the Basic Status Code to which it applies. [1]
The subjects are defined as follows:
The meaning of the "detail" field depends on the class and the subject, and are listed in RFC 3463 and RFC 5248.
A server capable of replying with an Enhanced Status Code MUST preface (prepend) the Text Part of SMTP Server responses with the Enhanced Status Code followed by one or more spaces. For example, the "221 Bye" reply (after QUIT command) MUST be sent as "221 2.0.0 Bye" instead. [1]
The Internet Assigned Numbers Authority (IANA) maintains the official registry of these enhanced status codes. [2]
This section list some of the more commonly encountered SMTP Status Codes. This list is not exhaustive, and the actual text message (outside of the 3-field Enhanced Status Code) might be different.
"Transient Negative" means the error condition is temporary, and the action may be requested again. The sender should return to the beginning of the command sequence (if any).
The accurate meaning of "transient" needs to be agreed upon between the two different sites (receiver- and sender-SMTP agents) must agree on the interpretation. Each reply in this category might have a different time value, but the SMTP client SHOULD try again.
The SMTP client SHOULD NOT repeat the exact request (in the same sequence). Even some "permanent" error conditions can be corrected, so the human user may want to direct the SMTP client to reinitiate the command sequence by direct action at some point in the future.
Below is an example SMTP connection, where a client "C" is sending to server "S":
S: 220 smtp.example.com ESMTP Postfix C: HELO relay.example.com S: 250 smtp.example.com, I am glad to meet you C: MAIL FROM:<bob@example.com> S: 250 Ok C: RCPT TO:<alice@example.com> S: 250 Ok C: RCPT TO:<theboss@example.com> S: 250 Ok C: DATA S: 354 End data with <CR><LF>.<CR><LF> C: From: "Bob Example" <bob@example.com> C: To: Alice Example <alice@example.com> C: Cc: theboss@example.com C: Date: Tue, 15 Jan 2008 16:02:43 -0500 C: Subject: Test message C: C: Hello Alice. C: This is a test message with 5 header fields and 4 lines in the message body. C: Your friend, C: Bob C: . S: 250 Ok: queued as 12345 C: QUIT S: 221 Bye {The server closes the connection}
And below is an example of an SMTP connection in which the SMTP Server supports the Enhanced Status Code, taken from RFC 2034:
S: 220 dbc.mtview.ca.us SMTP service ready C: EHLO ymir.claremont.edu S: 250-dbc.mtview.ca.us says helloS: 250 ENHANCEDSTATUSCODES C: MAIL FROM:<ned@ymir.example.edu> S: 250 2.1.0 Originator <ned@ymir.example.edu> ok C: RCPT TO:<mrose@dbc.mtview.example.us> S: 250 2.1.5 Recipient <mrose@dbc.mtview.example.us> ok C: RCPT TO:<nosuchuser@dbc.mtview.example.us> S: 550 5.1.1 Mailbox "nosuchuser" does not exist C: RCPT TO:<remoteuser@example.edu> S: 551-5.7.1 Forwarding to remote hosts disabledS: 551 5.7.1 Select another host to act as your forwarder C: DATA S: 354 Send message, ending in CRLF.CRLF. ... C: . S: 250 2.6.0 Message accepted C: QUIT S: 221 2.0.0 Goodbye {The server closes the connection}