I found a page that gives some very interesting advice on how to write emails of application.
Writing Effective E-Mail: Top 10 Tips
Summary: This document offers 10 tips to help you write effective professional e-mails.
Follow these tips in order to give your recipients the information they need in order to act on your message sooner rather than later.
1. Write a meaningful subject line.
2. Keep the message focused and readable.
3. Avoid attachments.
4. Identify yourself clearly.
5. Be kind -- don't flame.
6. Proofread.
7. Don't assume privacy.
8. Distinguish between formal and informal situations.
9. Respond Promptly.
10. Show Respect and Restraint.