If all E-mail forwarder or E-mail maker will foloow below listed tips I think no one will be annoyed in reading emails. Below is the Email etiquette by ajbatac but I have seen this from htmy McLife :: annemich.net blogs to share with you
1. Be concise and to the point.
2. Answer all questions, and preempt further questions.
3. Use proper spelling, grammar & punctuation.
4. Make it personal.
5. Use templates for frequently used responses.
6. Answer swiftly.
7. Do not attach unnecessary files.
8. Use proper structure & layout.
9. Do not overuse the high priority option.
10. Do not write in CAPITALS.
11. Donâ€™t leave out the message thread.
12. Add disclaimers to your emails.
13. Read the email before you send it.
14. Do not overuse Reply to All.
15. Mailings > use the Bcc: field or do a mail merge.
16. Take care with abbreviations and emoticons.
17. Be careful with formatting.
18. Take care with rich text and HTML messages.
19. Do not forward chain letters.
20. Do not request delivery and read receipts.
21. Do not ask to recall a message.
22. Do not copy a message or attachment without permission.
23. Do not use email to discuss confidential information.
24. Use a meaningful subject.
25. Use active instead of passive.
26. Avoid using URGENT and IMPORTANT.
27. Avoid long sentences.
28. Donâ€™t send or forward emails containing libelous, defamatory, offensive, racist or obscene remarks.
29. Donâ€™t forward virus hoaxes and chain letters.
30. Keep your language gender neutral.
31. Donâ€™t reply to spam.
32. Use cc: field sparingly.
33. Do not use excessive punctuations
I do hope that upon reading this post you will be aware on all the email you are sending to your friends.