The Netiquette IQ list of SMTP Error Messages

 The Meaning of the Numbers

          All robust-email users encounter returned messages. When reading the reasons given for returns, a large percentage of the senders do not understand the explanations. The following list provides brief definitions for the most common email errors. These are important to reference from a Netiquette point of view, in case a late or resent message or unavoidable error happens to serve as a reason for issues such as missing deadlines or similar occurrences.

        A mail server will reply to every request a client (such as your email program) makes with a return code. This code consists of three numbers.

        The first number usually signifies whether the server accepted the command and if it could handle it. There are five possible values:

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

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.

5)   The server has encountered an error.

        The second number gives more information. These six errors are defined as follows:

·         0 A syntax error has occurred

·         1 Informational reply to a request

·         2 A referral to the connection status

·         3 and 4 are not generally used

·         5 References the status of the mail system and the mail server

        The last number is the best recognized and shows more detail of the mail transfer status. The list names ESMTP server response codes, as defined in RFC 821 extensions.

• 211 - A system status message
• 214 - A help message for a human reader follows.
• 220 - SMTP service ready
• 221 - Service closing
• 250 - Requested action taken and completed
• 251 - The recipient is not local to the server, but the server will accept and forward the message.
• 252 - The recipient cannot be verified, but the server accepts the message and attempts delivery.
• 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 it to go).
• 421 - The service is not available, and the connection will be closed.
• 450 - The requested command failed because the user’s mailbox was unavailable—for example, because it was locked. Try again later.
• 451 - The command has been aborted due to a server error.
• 452 - The command has been aborted because the server has insufficient system storage.

The following error messages (500–504) are for the email client.

• 500 - The server could not recognize the command due to a syntax error.
• 501 - A syntax error was encountered in command arguments.
• 502 - This command is not implemented.
• 503 - The server has encountered a bad sequence of commands.
• 504 - A command parameter is not implemented.
• 550 - The user’s mailbox was unavailable. Either it no longer exists, or the message was blocked for security or policy rules.
• 551 - The recipient is not local to the server.
• 552 - The action was aborted due to exceeded storage allocation.
• 553 - The command was aborted because the mailbox name is invalid.
• 554 - The transaction failed. There could be many reasons, such as an outage, software, or network failure         
  +++++++++++++++++++++++++++++++++++++++++
  
  You can view my new book page at www.amazon.com/author/paulbabicki
  
  Anyone who would like to review the book and have it posted on my blog or website, please contact me paul@netiquetteiq.com
   
  Please visit our websites 
  www.netiquetteiq.com
  www.tabularosa.net