public void quit() {
		try {
			if (this.isConnected() && !this.serverClosingTransmissionChannel) {
				this.sendAndCheck("QUIT");
			}
		} catch (final IOException ex) {
			LOGGER.warn("Failed to issue QUIT to {}", this.hostPort);
		}

		this.close();
	}
Quit and close down the connection. Ignore any errors.
<p>
It still closes the connection, but it does not send the QUIT command if a
421 Service closing transmission channel is received previously. In these
cases QUIT would fail anyway.

@see <a href="http://tools.ietf.org/html/rfc5321#section-3.8">RFC 5321
     Terminating Sessions and Connections</a>
src/test/java/de/gessnerfl/fakesmtp/smtp/client/SmartClient.java