444 No Response - Nginx 449 Retry With - Microsoft 450 Blocked by Windows Parental Controls - Microsoft 499 Client Closed Request - Nginx
506 Variant Also Negotiates - RFC 2295; experimental
Non-authentication POP3 protocol error (reply code “-ERR”, except authentication).
POP3 authentication error.
Represents an SMTP authentication error.
Represents an SMTP command syntax error (error code 500)
Represents a fatal SMTP error (error code 5xx, except for 500)
Unexpected reply code returned from server.
Raises when there is an argument for a switch which takes no argument.
Raises when a switch with mandatory argument has no argument.
Raises when the given argument does not match required format.
Raises when the given argument word can’t be completed uniquely.