To get a reply to an email you sent, the key is to make the email rather short and slightly positive or negative. The Atlantic's Adrienne LaFrance has gone through the analysis done by email-efficiency service Boomerang on what makes the perfect email.
Boomerang found that emails that were slightly positive or slightly negative were most likely to get responses. Asking a couple of questions is good, but more than three starts working against you. "Flattery works, but excessive flattery doesn't," they wrote in a blog post about the findings. "We also don’t advise penning day-ruining screeds."
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So, you know, play it cool. But not too cool. Also, no need to write long. The optimum length for an email is 50 to 125 words.