SMTP Protocol Error Codes
The following are SMTP protocol error codes given in RFC821.
RFC is an Internet “standards” term meaning “Request For Comment.” RFCs are documents that define standards or proposed
When these occur, contact your network administrator.
E421 <domain>
Service not available, closing transmission channel.
This may be a reply to any command if the service knows it must shut down.
E450 Requested mail action not taken: mailbox unavailable.
Example: the mailbox is busy.
E451 Requested action aborted:
local error in processing
E452 Requested action not taken:
insufficient system storage
E500 Syntax error, command unrecognized.
This may include errors such as command line too long.
E501 Syntax error in parameters or arguments
E502 Command not implemented
E503 Bad sequence of commands
E504 Command parameter not implemented
E550 Requested action not taken: mailbox unavailable.
Example: mailbox not found, no access
E551 User not local; please try
E552 Requested mail action aborted: exceeded storage allocation
E553 Requested action not taken: mailbox name not allowed Example: Mailbox syntax incorrect
E554 Transaction failed