Background service downloading mail confusion

Question

I have a Helper class and method where I download mails via javamail. It's working fine inside AsyncTask.

Now I want to implement background service which will be able to:

• run on demand
• run periodically if not running on demand
• has a method where I can know it's ended
• work both inside and outside the application (for example I press the refresh button and the same service is called)

I currently have created a Service with ScheduledThreadPoolExecutor and I can run that periodically (every 5 minutes). I just don't know how to run that on demand.

Should I use an Intent service, just Service, or even SyncAdapters? What would be the best option?

This is what I have so far:

public class BackgroundLoadingService extends Service {
@Override
public IBinder onBind(Intent intent) {
    return null;
}

@Override
public void onCreate() {

    final ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(1);

    executor.scheduleAtFixedRate( new Runnable() {

        @Override
        public void run() {
            Log.i("LocalService", "onCreate");

            if (isOnline(BackgroundLoadingService.this))
            {
                getEmails(BackgroundLoadingService.this,"test",true);
            }

        }
    }, 1, 60*5, TimeUnit.SECONDS );
    super.onCreate();
}

@Override
public int onStartCommand( final Intent intent, final int flags, final int startId ) {
    Log.i("LocalService", "onstartcommand");

    return Service.START_STICKY;
}

}