Electronic mail in Computer Network

Electronic mail:

Electronic Mail (e-mail) is very popular nowadays to exchange messages between several users. It has its conventions and styles. The standard for e-mail is written in RFC 822.

Architecture of e-mail:

E-mail system normally consists of two systems:
1. User-Agent: It allows the user to send and receive e-mail.
2. Message Transfer Agent: It is responsible for moving messages from source to destination.

Services Provided by e-mail:

i. Composition: It refers to the process of creating a new message. It may have its text editor or any other normal text editors can also be used. The receiver address and subject of the message are to be provided by the sender.
ii. Reply: In the case of a reply the receiver’s address is automatically substituted by the user agent. The content of the message is also sometimes replaced by the user agent.
iii. Reading: The user agent checks the e-mail in the incoming mailbox. Most of the user agents display a one-line summary of each of the incoming messages. The summary contains the following fields:

a. Message Number
b. Flag: It indicates whether the mail is new, already read but not replied etc.
c. Size: It indicates how long (in terms of bytes) the message is.
d. Sender
e. Subject
iv. Forwarding: It means to transfer an already received message from a sender to a third party.

v. Transfer: It refers to moving messages from the sender to the receiver. In most cases, this requires establishing a logical connection between the two endpoints, delivering the message, and releasing the connection. The e-mail system automatically does these for the user.
vi. Reporting: It is part of the service through which the sender is intimated about the delivery status of the message.
vii. Disposition: After the message is received the recipient can read the message. It can forward it and it can delete the message also.
viii. Handling mail-box: The user agent normally create two mail-boxes:
a. inbox – The inbox keeps all the incoming mails.
b. outbox – The outbox keeps all the outgoing mails.

Structure of e-mail:

The basic structure of e-mail is almost the same as postal mail. It has two parts:
i. Envelope: It encapsulates the message. It contains the sender address, receiver address, priority, security level, etc. required for transporting the message from source to destination. The message transport agent uses the envelope for routing the mail.
ii. Message: The message is encapsulated by the envelope. It has two parts:
a. Header: The header contains the control information for the user agent.
b. Body: The body which contains the actual information to be read by the human recipient.