444 No Response - Nginx 449 Retry With - Microsoft 450 Blocked by Windows Parental Controls - Microsoft 499 Client Closed Request - Nginx
OpenTimeout, a subclass of Timeout::Error, is raised if a connection cannot be created within the open_timeout.
ReadTimeout, a subclass of Timeout::Error, is raised if a chunk of the response cannot be read within the read_timeout.
WriteTimeout, a subclass of Timeout::Error, is raised if a chunk of the response cannot be written within the write_timeout. Not raised on Windows.
Represents a fatal SMTP error (error code 5xx, except for 500)