SMTP/ESMTP error codes

    How often do you get "FATAL ERROR: Could not send your message. Error #550" when sending email? What does "Error #550" mean?

    In this section you will find short description of SMTP/ESMTP error codes and error messages you need to know to understand why your email was not send and what to do.

    The structure of SMTP error codes

    A mail server will reply to every request your mail client (such as your email program, like Outlook Express, Eudora or Atomic Mail Sender etc.) makes with a return code. This code consists of 3 digits:

    The first digit tells whether the server accepted the command and if it could handle it. There are 5 possible values:

    1. Mail server has accepted the command, but does not yet take any action. A confirmation message is required.
    2. Mail server has completed the task successfully without errors.
    3. Mail server has understood the request, but requires further information to complete it.
    4. Mail server has encountered a temporary failure. If the command is repeated without any change, it might be completed. Try again, it may help!
    5. Mail server has encountered a fatal error. Your request can't be processed.

    Second digit tells more. There are six possible values:

    1. Syntax error
    2. Information reply (for example to HELP request)
    3. This digit refers to the status of connection
    4. non-used
    5. non-used
    6. This digit refers to the status of the mail server

    The third digit tells more then second again. It shows more graduations of the mail transferring status.

    Combination of these three digits gives us detailed list of ESMTP server response codes, as laid down in RFC 821 and later extensions (Check the RFC index for further mail-related RFCs).

    Error code SMTP/ESMTP error message description
    211 System status, or system help reply
    214 Help message (information on how to use the receiver or the meaning of a particular non-standard command; this reply is useful only to the human user)
    220 Service ready
    221 Service closing transmission channel
    250 Requested mail action okay, completed
    251 User not local; will forward to
    354 Start mail input; end with .
    421 Service not available, closing transmission channel (this may be a reply to any command if the service knows it must shut down)
    450 Requested mail action not taken: mailbox unavailable (e.g., mailbox busy)
    451 Requested action aborted: local error in processing
    452 Requested action not taken: insufficient system storage
    500 Syntax error, command unrecognized (this may include errors such as command line too long)
    501 Syntax error in parameters or arguments
    502 Command not implemented
    503 Bad sequence of commands
    504 Command parameter not implemented
    550 Requested action not taken: mailbox unavailable (e.g., mailbox not found, no access)
    551 User not local; please try ( this message indicates that the recipient specified in the RCPT command is not locally hosted on the server and relaying options prevent the message being forwarded to the recipient.)
    552 Requested mail action aborted: exceeded storage allocation
    553 Requested action not taken: mailbox name not allowed (e.g., mailbox syntax incorrect)
    554 Transaction failed

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