Email Etiquette Simplified

One of the classes that I teach at my church is Social Media Communication. This class is geared toward young adults that are heading out into the business or ministry world for the first time. Most of these kids are the last to have any recollection of a time before cell phones and computers were everywhere and need to be reminded that there are many of us that are 'old fashioned' and follow etiquette rules that they may have no idea about. The following is an excerpt from my class, focusing on email:

Email Etiquette (for business/ministry/volunteer situations)

A) Clear, direct subject
B) Should look like a regular letter, like you learned in school
C) Don't "Reply All" unless it's required for the situation. Follow up information should go directly to the person that you have follow up with.
D) Don't use slang
E) Use correct punctuation. More than 1 exclamation point is probably too much. 
F) PROOF READ. Spell check is ok but it can't and won't catch every mistake.
*two, too, to, their, there, they're, breath, breathe, more.......
G) Grammar! Verb tense, run on sentences, and other mistakes can usually be found when you read it out loud. If it's awkward, fix it.
H) Don't switch fonts, text colors, etc., in the body of an email.
I) You should respond to most email within 24 hours, weekends excluded.

What would you add? Is there something that twenty-somethings need to know about emailing in business situations that I've forgotten? Let me know in the comments!