E-mail has become a common medium for communication in business - it's fast, easy and confinement. However, it comes with its own set of pitfalls.
Primarily, e-mail is used too frequently, and to casually. Think of e-mail as being the equivalent of a written memo. Do not use it frivolously, and do not use it causally.
Especially, considerer the difficulty in written communication: you may not "come across" as intended, and there is no way to gauge a reader's reaction. Many misunderstandings have arisen as the result of a written message.
EN: A few bits of advice are given that can best be summarized as "tend to your communication skills." Choose a clear subject, be brief and to the point, mind your spelling and grammar, etc. This is beyond the scope of the present subject.
Also, consider the receiver's communication preferences. Some individuals aren't receptive to e-mail: they may not read it promptly, or at all. A message may be transmitted the moment you click "send," but that doesn't mean it has been received (and read) by the recipient.
As a recipient, reply to e-mail in a timely manner - preferably within the same business day, or within 24 hours - and consider whether "reply all" is necessary (use it conservatively).