respondez sil vous plait

Is there some kind of email etiquette that I'm not party to? You know, the one where people feel they don't have to respond? It's a little like nodding on the end of the phone - you know you're doing it, but the person on the other end doesn't.

Because I've got a Mac, I can't seem to set my email to have a "read receipt" so unless somebody replies, I have no way of knowing if they've got my email, which can be a tad on the annoying side. 

That's my whinge for the day. I'll be off now. To email some friends who always reply!