Bay of Isles Computers
63B Dempster Street
Esperance WA 6450
Ph: 08 9071 5542
Fax: 08 9071 5549
boic@boic.net.au
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Understanding Email Error Messages
 Thanks to
Microsoft Communique March 2001
It's all very well for remote systems to report back to you; it's another thing to be able
to understand what's being reported. Most errors related to undelivered email are messages
sent from the SMTP (Simple Mail Transport Protocol) Server. Your email program might state
succinctly:
Could not send your message. Error 421.
With messages such as this, it's not clear why it could not be sent, whose fault it was,
or what might be done to resolve the problem. All you have is an esoteric number to explain
the failed delivery of your message.
To regain your precious screen space, you can simply dismiss the message window with a click
of your mouse. On the other hand, you can also check below to find out the meaning of the
messages.
The secret meaning of the codes.
Mail servers reply to every request a client (such as your email program) makes.
Their replies are in the form of a three number code.
The first number
The first number generally tells if the server has accepted the command and if it can handle it.
The five possible values are:
- 1 The server accepts the command but is yet to take action pending a
confirmation message.
Currently this process is not used.
- 2 The server completed the task successfully.
- 3 The server understands the request but requires further information to
complete it.
- 4 The server encountered a temporary failure. If the same command is repeated,
it might succeed.
Rarely used.
- 5 The server encountered an error.
The second number
The second number gives more information. The six possible values are:
- 0 A syntax error has occurred.
- 1 An informational response: for example,
responding to a Help request.
- 2 Refers to the connection status.
- 3 Unspecified.
- 4 Unspecified.
- 5 Refers to the status of the mail system as a whole and the mail server
in particular.
The last number.
The last number is the most specific, showing the mail transfer status in detail.
The codes for Extended Simple Mail Transport Protocol are listed below and are in
accordance with the Internet specification RFC 821 (and later extensions).
ESMTP server response codes
- 211
- A system status message
- 214
- A help message for a human reader follows
- 220
- Service ready
- 221
- Service closing
- 250
- Requested action taken and completed
- 251
- The recipient is not local to the server but it will accept and forward the message
- 252
- The recipient cannot be verified (VRFY) but the server will accept and try to deliver
the message
- 354
- Start message input and end with . (This indicates, nevertheless, that the
server is ready to accept the message itself)
- 421
- The service is not available - the connection will be closed
- 450
- The requested command failed because the user's mailbox was unavailable (It may be
locked or already in use, for example)
- 451
- The command was aborted due to a server error
- 452
- The command was aborted because the server has insufficient system storage
- 500
- The server could not recognise 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 requested command failed becuse the user's mailbox was unavailable (for example,
because it was not found or because the command was rejected for policy reasons)
- 551
- The recipient is not local to the server (The server then gives a forward address to try)
- 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
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