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Posted by on Jul 17, 2017 in Blog, Tips & Tricks |

SMTP Error Codes – what do they mean?

SMTP Error Codes – what do they mean?

From time to time you may experience error message when sending emails. This can be for a number reasons. Below is a list of the most common errors.

SMTP 550: Permanent Failure for One or More Recipients?

The most common generic error message. It means the email could not be delivered. This could be for a number of reasons.

  • The users mailbox is full
  • The users mailbox doesn’t exist anymore
  • Blocked by spam due to the content or by the senders network
  • The senders network maybe blacklisted.

What can you do?

If possible, try to contact the recipient by other means. If the error message points to a specific blacklist or spam filter, do try to contact the list or filter administrator.

Failing all this, you can always explain the unfortunate situation to your email provider. They may be able to contact their colleague at the receiving end and get the situation sorted.

List of SMTP Error Codes (with Explanations)

An ‘SMTP’ error’s three numbers get us a detailed list of ‘ESMTP’/SMTP server response codes, as laid down in RFC 821 and later 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. The best message of them all.
  • 251 – The recipient is not local to the server, but the server will accept and forward the message.
  • 252 – The recipient cannot be VRFYed, but the server accepts the message and attempts delivery.
  • 354 – Start message input and end with .. 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).
  • 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. Not your fault. Maybe let the admin know.
  • 452 – The command has been aborted because the server has insufficient system storage.
  • 455 – The server cannot deal with the command at this time.

The following error messages (500-504) usually tell you that your email client is broken or, most commonly, that your email could not be delivered for one reason or another.

  •  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.
  • 521 – This host never accepts mail; a response by a dummy server.
  • 541 – The message could not be delivered for policy reasons—typically a spam filter. (Only some SMTP servers return this error code.)
  • 550 – 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).
  • 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. Blame it on the weather.
  • 555 – The server does not recognize the email address format, and delivery is not possible.
  • 556 – The message would have to be forwarded, but the receiving server will reject it.

Original content source: Lifework