Composing E-mail Messages - - Explains the steps taken in composing, replying to, and sending messages.
Dan's Mail Format Site - - Includes guidelines on quoting and attachments, information about headers, and mail client configuration.
E-mail Replies - - Tips on implementing mail policies, etiquette, rules and management software to improve the effectiveness of business communications.
E-mail Resources - - Tips and tricks, beginner's articles, software downloads, spam management, and general help. From About.co.
eMailman - - Coverage of all issues related to the usage of e-mail.
Flash Your E-mail - - Spice-up your messages with a Flash signature file.