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Webfoot.com: A Beginner's Guide to Effective Email Format
This guide explains what types of formats you should use in your email messages to insure the receiver will receive your message as intended. This website covers fancy text, extended character sets, web links, punctuation and quotation...
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A Beginner's Guide to Effective Email: Intonation
A good site as a resource for changing tone and voice in the written medium of email. Discusses asterisks, capital letters, punctuation, whitespace, and lower-case letters.
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A Beginner's Guide to Effective Email: Acronyms & Jargon
An interesting and fairly detailed list of many of the acronyms that are used in email. Also discusses some unique internet/email "jargon," such as "spam."
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A Beginner's Guide to Effective Email: Gestures
Another site giving advice to beginning email users; this one deals with gestures in emails, such as smileys, pause equivalents, and creative punctuation.