Inside Higher Ed: A Primer on Electronic Communication — A bit wordy, but several good suggestions including:
1. Write a clear and descriptive subject line.
2. Address the person politely.
3. State your reason for contact.
4. Read your letter (before sending).
5. Get in touch again in a week if you receive no response.
Also, NY Times: ‘Yours Truly,’ the E-Variations — There’s lots more to ending an email than Sincerely,.