|250||The mail server has successfully delivered the message!|
|420||Timeout communication problem encountered during transmission.|
|421||Service not available, closing control connection. This may be a reply to any command if the service knows it must shut down.|
Requested action not taken – The mailbox was unavailable at the remote end.
A secondary SMTP error code may follow “450” to refine the reason for the failure to transmit the message, e.g. “SMTP error 450".
Requested action aborted – Local error in processing.
Requested action delayed – Local problem
<IP_Address> has recently sent spam.
|452||Requested action not taken – Insufficient storage.|
|471||This is a local error with the sending server and is often followed with "Please try again later."|
|550||Requested action not taken. File unavailable (e.g., file not found, no access). It usually defines a non-existent email address on the remote side.|
|554||SMTP 5.7.1 is basically a rejection from the Recipient Domain.|
|The address in MAIL FROM appears to have insufficient submission rights, or is invalid, or is not authorized with the authentication used; the address in a RCPT TO command is inconsistent with the permissions given to the user; the message data is rejected based on the submitting user.