Here’s a nice article which we could all learn from. 9 Tips for Emailing Important People on Six Revisions points out that as most emails you send are to ask someone about something, making it easy for them to respond is a win-win strategy. So here goes. Firstly, people might only have time to write a short reply, and might feel guilty about that if your email was long. So keep yours short in the first place. Then there’s the need to give your email a clear purpose. Don’t waffle! Send your message just to the person who it’s aimed at. Don’t copy it to others just to show you’re doing your job. The main recipient might mistakenly leave it to the others to reply.
There are plenty more ideas in the article, which is worth a read.