When is e-mail NOT an appropriate form of communication to use?
E-mail is not an effective means of communication when :
Your message is long and complicated or requires additional discussion that would best be accomplished face-to-face. For example, if you want feedback from your supervisor on your work or if you are asking your professor a question that requires more than a yes/no answer or simple explanation,you should schedule a meeting instead.
Information is highly confidential. E-mail is NEVER private! Keep in mind that your message could be forwarded on to other people without your knowledge. A backup copy of your e-mail is always stored on a server where it can be easily retrieved by interested parties,even when you have deleted the message and think it is gone forever.