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SMTP Server Response Codes

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SMTP servers use to respond to commands using a defined set of codes.?This page is a small guide to the codes mail servers may produce when you try to send mail along with their meanings.?They are part of the SMTP protocol (the set of rules used to send emails).

The Meaning of the Codes
A mail server will reply to every request a client (such as?MaxBulk Mailer) makes with a return code. This code consists of three numbers.

?The first generally tells whether the server accepted the command and if it could handle it. The five possible values are:

1: The server has accepted the command, but does not yet take action. A confirmation message is required.

2: The server has completed the task successfully.

3: The server has understood the request, but requires further information to complete it.

4: The server has encountered a temporary failure. If the command is repeated without any change, it might be completed.

5: The server has encountered an error.

?The second number gives more information. Its six possible values are:

0: A syntax error has occured.

1: Indicates a informational reply, for example to a HELP request.

2: Refers to the connection status.

3 and 4 are unspecified.

5: Refers to the status of the mail system as a whole and the mail server in particular.

?The last number is even more specific and shows more graduations of the mail transfer status.

This leads us to the detailed list of ESMTP server response codes, as layed down in?RFC 821?and later extensions.

CodeDescription

211System status, or system help reply.214Help message (for a human reader follows).220SMTP Service ready (or Ready to start TLS).221SMTP Service closing transmission channel.250OK, queuing for node?node?started. Requested mail action okay, completed (Requested action taken and completed).251OK, no messages waiting for node?node. User not local, will forward to?forwardpath(The recipient is not local to the server, but the server will accept and forward the message).252Cannot VRFY user (e.g., info is not local), but will take message for this user and attempt delivery (The recipient cannot be verified, but the server accepts the message and to attempt delivery).253OK,?messages?pending messages for node?node?started.354Start mail input; end with <CRLF>.<CRLF>. This indicates that the server is ready to accept the message itself (after you have told the server who the message is from and who you want it to be sent to).355Octet-offset is the transaction offset.421Domain?service not available, closing transmission channel (The service is not available and the connection will be closed).432A password transition is needed.450Requested mail action not taken: mailbox unavailable.
ATRN request refused (The requested command failed because the user's mailbox was unavailable, for example because it was locked).451Requested action aborted: local error in processing. Unable to process ATRN request now (The command has been aborted due to a server error. Not your fault. Maybe let the admin know).452Requested action not taken: insufficient system storage (The command has been aborted because the server has insufficient system storage, it happens sometimes when sending to a lot of recipients in Bcc mode).453You have no mail.454TLS not available due to temporary reason.
Encryption required for requested authentication mechanism.458Unable to queue messages for node?node.459Node?node?not allowed:?reason.500Command not recognized:?command. Syntax error (The server could not recognize the command due to a syntax error).501Syntax error, no parameters allowed (A syntax error was encountered in command arguments).502Command not implemented (This command is not implemented).503Bad sequence of commands (The server has encountered a bad sequence of commands).504Command parameter not implemented (A command parameter is not implemented).505Authentication required521Machine?does not accept mail.530Must issue a STARTTLS command first.
Encryption required for requested authentication mechanism.534Authentication mechanism is too weak.538Encryption required for requested authentication mechanism.550Requested action not taken: mailbox unavailable (The requested command failed because the user's mailbox was unavailable, for example because it was not found, or because the command was rejected for policy reasons).551User not local; please try?forwardpath?(The recipient is not local to the server. The server then gives a forward address to try).552Requested mail action aborted: exceeded storage allocation (The action was aborted due to exceeded storage allocation).553Requested action not taken: mailbox name not allowed (The command was aborted because the mailbox name is invalid).554Transaction failed.571No external routing allowed, remote sending only allowed with authentication (Illegal relay, missing authentication, RBL/blacklisting)572Bounces are blocked due to system abuse by spammers

Blue rows correspond to successfull responses.
Rose rows correspond to delivery errors
Red rows corresppond to server errors.