These probably aren't really patterns in some cases or have been documented elsewhere (FAQs, books for dummies, etc.), the following EmailNetiquettePatterns cover some important recurring themes in e-mail:
- TrimYourPosts
- FitFormatToAudience (plain text? html? .doc format?)
- MeaningfulSubjectLine
- LurkBeforeYouLeap
- AskBeforeAttaching
- LessThanEightyColumns
- SixLineSigLimit
- StandardSigDelimiter
- PrivateResponsePrivateReply
- PrivateResponseVisibleReminder
- KeepItCivilStupid
- MixedCaseMessage
- SplitLongBlocks
- UncuddledParagraphs
- ProofBeforePosting
- ItsWiseToRevise
- AssumeStupidityNotMalice
- ConquerWithCompassion
- RetireGracefully
- ReplyBelowOriginal
- ChangeTheSubjectIfYouChangeTheSubject
- ThreadsStartsWithNewMessages
- EmailAdulteration
Note that most of these patterns apply to mailing lists (and maybe also to UseNet newsgroups), not to general person-to-person or office e-mail.