Never start with, hi or hello, followed by nothing else, expecting a response back. It’s not a two way chat initially. Instead, greet or introduce your self, and then, write everything you want to say including what exactly you want to discuss or enquire about. You are more likely to get a response when you include the details. If you don’t get a response, you can follow up in a few days or weeks as some inboxes like mine can be inundated with messages. Thank me later.