noop method
Trigger a noop (no operation).
A noop can update the info about the currently selected mailbox and can be used as a keep alive. Also compare idleStart for starting the IMAP IDLE mode on compatible servers.
Implementation
Future<Mailbox> noop() {
final cmd = Command('NOOP');
return sendCommand<Mailbox>(cmd, NoopParser(this, _selectedMailbox));
}