Electronic Mail Etiquette - David Harris discusses email addresses, subject lines, message length and content, replies, digital signatures, courtesy and Emoticons.Dynamoo's Email Etiquette - Good and bad email etiquette explained.
Spam Is Not the Worst of It - Email etiquette and related gripes from the Unquietmind. Discusses common annoyances ranging from bad spelling to sending chain letters and other junk.
About Netiquette - Advice on civility, manners and the internet, with an emphasis on email.
All e-mail messages are not to be treated equally - Article that cuts through some email myths [from atlanta.bcentral.com].
I Will Follow - E-mail Etiquette - Guidelines for writing emails. Covers quoting, smilies, salutations, digital signatures, privacy, abbreviations, flame email and newsgroups.