Review: You Send Me: Getting It Right When You Write Online 
This book addresses the issues of online writing and particularly writing e-mail, which should concern all us who spend a good chunk of our days in front of a computer screen creating and replying to e-mail messages. The book is structured in three parts: 'The virtual mensch,' 'Alpha mail,' and 'Words of passage.'
Crawley, Charles R. Technical Communication Online (2002). Articles>Reviews>Style Guides>Email