Sends a 'NOOP' command to the server.
The 'callback' parameter specifies a function which will be called when the operation completes (or an error is encountered). If the 'callback' parameter is not specified, then the method will block and will not return until the operation completes (or an error is encountered).
The callback for this method is defined as:
'err' is the error that occurred. If there was no error, then 'err' is 'null'.
'err' has 2 properties which hold detailed information:
This method sends an IMAP 'NOOP' command to the server. This is useful when the connection needs to be kept alive for long periods of time. (Normally, servers break the connection automatically after 30 minutes of inactivity).