Harry Potter Question?

Okay so I know a little bit about Harry Potter so I know that yesterday the train left for Hogwarts. I also noticed that people on Twitter were saying things like "How am I suppose to get my acceptance letter if there is no post on Sundays?" Other people would say "You get your acceptance letter way before that, it's the train that leaves today." Now I'm pretty sure they are right but then I stumbled across someone saying "If you have muggle parents it's sent via muggle post. However, Hogwarts knows if you open the letter or not so they will continue to send them (via owl post) until you open it." Then that got me thinking, maybe they're right. In the Philosopher's Stone, Harry was bombarded with letters and got them daily. So maybe both views are somewhat right? I honestly don't know. Who was correct?