Electronic mail is exactly what it says it is.
It is a way for a person to commuicate with another person as one would in a posted letter. A more accurate description is that it is an asynchronous electronic communication medium used primarily for the transfer of text. The second part of the definition deals with the type of information that is transmitted. I mention this because you may already have experienced receiving an e-mail message with an attachment and you find that the message opens without problems but the attachment seems inaccessible. This is not a problem with your e-mail, you probably just don't have the appropriate software to open the attachment.