Boomerang, which makes an awesome email tool for Gmail users, studied emails that got the most responses.
• Use shorter sentences with simpler words. Third grade reading level works best.
• Include 1 to 3 questions in your email — max.
• Subject lines should be 3 to 4 words.
• Use a slightly positive or slightly negative tone. Both outperform a completely neutral tone.
• Take a stand. Opinionated messages see higher response rates than objective ones.
• Try to keep messages between 50-125 words.
So, if you are wondering why people aren't responding to your emails, consider the above and good luck!