Email is a good way to get your message across when :
You need to get in touch with a person who is hard to reach via telephone, does not come to campus regularly, or is not located in the same part of the country or world (for instance, someone who lives in a different time zone).
Email (or e-mail) communication can be defined as the exchange of short informational messages between at least two people over a computer network. These messages containing plain text, images or document attachments are delivered through email web-based services like Gmail, Outlook, or Yahoo.
The information you want to share is not time-sensitive. The act of sending an email is instantaneous, but that does not mean the writer can expect an instantaneous response. For many people, keeping up with their email correspondence is a part of their job, and they only do it during regular business hours. Unless your reader has promised otherwise, assume that it may take a few days for them to respond to your message.
You need to send someone an electronic file, such as a document for a course, a spreadsheet full of data, or a rough draft of your paper.
You need to distribute information to a large number of people quickly (for example, a memo that needs to be sent to the entire office staff).
You need a written record of the communication. Saving important emails can be helpful if you need to refer back to what someone said in an earlier message, provide some kind of proof (for example, proof that you have paid for a service or product), or review the content of an important meeting or memo.