The email messages have a text message and several identifiers for the recipient and sender. They also have the possibility to specify a subject for the messsage and you can also attach files to the message.
Those identifiers are called email addresses and they are given by the email service companies. Those companies are the owners of the email servers and they are responsible for sending and receiving email messages without interruption.
The email clients include a contact manager to search the recipients email addresses easily. They also have spell checkers in several languages and automatic message labelling and filtering systems.