Non-authentication POP3 protocol error (reply code “-ERR”, except authentication).
POP3 authentication error.
Unexpected response from the server.
ReadTimeout, a subclass of Timeout::Error, is raised if a chunk of the response cannot be read within the read_timeout.
Represents an SMTP authentication error.
Represents SMTP error code 420 or 450, a temporary error.
Represents a fatal SMTP error (error code 5xx, except for 500)
Unexpected reply code returned from server.
Command is not supported on server.