private void acquireConnectionPermit() {
		try {
			// block if too many connections are open
			connectionPermits.acquire();
		} catch (final InterruptedException consumed) {
			Thread.currentThread().interrupt();
		}
	}
Accept connections and run them in session threads until shutdown.
src/main/java/de/gessnerfl/fakesmtp/smtp/server/BaseSmtpServerRunnable.java