Email and Etiquette

First off, I like email.
I know email isn't as cool with the younger crowd anymore, they'd rather have a Facebook message, and that's fine too but I still really like my email.

You can contact several people at once, you can spell check it, and you can attach whatever you need to! But I have found that I've run into a question of etiquette that I'm not sure of anymore. If you get an announcement email, or a request email, do you need to respond or acknowledge it? I recently sent out several announcements about a Shakespeare theatre production I'm involved with to invite some local high school teachers and their students to auditions, and no one acknowledged receiving the email. Now, there was nothing in the email asking them to respond, but I just would have thought at least one of them would have said "Cool! Thanks!" (Unless the whole thing was really lame... also possible!) When I contact colleges with general updates and information usually at least half of them will respond with a simple "Thank you"... so I know they received it. So is that something you should do? Or not? Or does it depend on the email?

So then, if you're contacted by a school via email do you need to respond? I guess I would always encourage it... since usually it's not spam- and if you're not interested in the school you can use the response as an opportunity to tell them you're not interested. Otherwise if you're undecided use your response to ask more questions and learn more, and more importantly, get a feeling about the personnel at the college. Does it take them 3 minutes or 3 days to respond to your email?

As for me, I generally like a basic response to emails I send out- even if it's just a 'yes' or a 'thank you'... and that's it! But I don't know if that's to be expected or not from a majority?

Can anyone enlighten me a little bit please??