Electronic mail Architecture and Services
An Electronic mail is the most widely used tool in the present world for fast and reliable communication. It is based on RFC 882. It has two components from architectural point of view.
User agents are local programs that provide that can provide Command based or menu based or graphical method for interacting with email system.
Message transfer agents are system daemons (processes that run in background) that move e-mail through the system.
An Email system support five basic functions
1) Composition: Helps in creating message and answers, supports many functions such as insertion of address after extraction from the original message during replying etc.
2) Transfer: Causes moment of message to the destination. Connection establishments and passage of message is done here.
3) Reporting: Do involve in reporting the origin of email whether it is delivered, lost or abandoned.
4) Displaying: Sometimes the e-mails come with attachments. The attached files may be in different format, maybe there are images or audio clips or they may be pdf files. Whenever the email encounters such files in the attachment, it should invoke certain programs called PLUG-INS and display them without user interference.
5) Disposition: This constitutes the last stage, The email may be saved, forwarded, replied, deleted etc… The final action is disposition.
Additional features of E-mail system
Forwarding: Forward email to another email ID.
Mail box: Storing/retrieving email
Mailing list: Send copies to the entire email list.
Other functions: CC : carbon copy
BBC : Blind copy
Electronic mail User Agent (UA)
It is a program that accepts wide varieties of commands that support
- Replying to message
- Support manipulation of mail box.
Some UA have memo/icon driven interface while other may use commands.
Sending an Electronic mail
User must provide a message, destination address and other data.
- Messages are generated using built in editors.
- Destination address follows a format user@dns-address.
- Instead of entering the full address, one can write alias.
- Email can also be send to a mailing list.
Reading Electronic mail
When a user agent in invoked, it looks for mail box and display the information
- # – No. of the mail.
- Flags – Status: K read already, N: new
- Bytes : Size
- Sender – Sender name email
- Subject – information at header.
Each line of the display is extracted from the mail envelope or corresponding header.
Thus user can use any of the following commands
- R : Reply
- C: Compose
- D : Delete
- F : Forward
- E : Exit