This list is a copy of the Theory of Reply Codes as discussed in RFC821 (the Internet Mail Standard).
The three digits of the reply each have a special significance. The first digit denotes whether the response is good, bad or incomplete. An unsophisticated sender-SMTP will be able to determine its next action (proceed as planned, redo, retrench, etc.) by simply examining this first digit. A sender-SMTP that wants to know approximately what kind of error occurred (e.g., mail system error, command syntax error) may examine the second digit, reserving the third digit for the finest gradation of information.
Positive Completion Reply (2.x.x):
The command has been accepted, but the requested action is being held in abeyance, pending confirmation of the information in this reply. The sender-SMTP should send another command specifying whether to continue or abort the action. [Note: SMTP does not have any commands that allow this type of reply, and so does not have the continue or abort commands.]
|200||(nonstandard success response, see rfc876)|
|211||System status, or system help reply|
|220||<domain> Service ready|
|221||<domain> Service closing transmission channel|
|250||Requested mail action okay, completed|
|251||User not local; will forward to <forward-path>|
|283||The Gordano server is configured so that messages aren't being saved. The FROM and TO address are taken from the e-mail message headers|
Positive Intermediate (3.x.x):
The command has been accepted, but the requested action is being held in abeyance, pending receipt of further information. The sender-SMTP should send another command specifying this information. This reply is used in command sequence groups.
|354||Start message input and end with <crlf>.<crlf>. This indicates that the server is ready to accept the message itself (after you have told it who it is from and where you want to to go).|
Transient Negative Completion Reply(4.x.x):
The command was not accepted and the requested action did not occur. However, 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). It is difficult to assign a meaning to "transient" when two different sites (receiver- and sender- SMTPs) must agree on the interpretation. Each reply in this category might have a different time value, but the sender-SMTP is encouraged to try again. A rule of thumb to determine if a reply fits into the 4yz or the 5yz category (see below) is that replies are 4yz if they can be repeated without any change in command form or in properties of the sender or receiver. (E.g., the command is repeated identically and the receiver does not put up a new implementation.)
|421||<domain> Service not available, closing transmission channel|
|450||Requested action not taken; mailbox unavilable or busy|
|451||Requested action aborted, local error in processing|
|452||Requested action not taken, insufficient system storage|
Permanent Negative Completion Reply (5.x.x):
The command was not accepted and the requested action did not occur. The sender-SMTP is discouraged from repeating the exact request (in the same sequence). Even some "permanent" error conditions can be corrected, so the human user may want to direct the sender-SMTP to reinitiate the command sequence by direct action at some point in the future (e.g., after the spelling has been changed, or the user has altered the account status).
|500||Syntax error, command unrecognized. Also command line too long|
|501||Syntax error in paramaters or arguements|
|502||Command not implemented|
|503||Bad sequence of commands|
|504||Command parameters not implemented|
|521||<domain> does not accept mail (see rfc1846)|
|550||Action not taken. Mailbox unavailable. Not found, not accessible|
|551||User not local, please try|
|552||Exceeded storage allocation|
|553||Mailbox name not allowed. Mailbox syntax may be incorrect|