Electronic Mail

Functionality First software allowed a user to send some text to another user connected to Internet; Current systems allow a user to: Send a message to several recipients; Send other type of data beside text Send messages to a user on a network outside the Internet; Send a message to a program, which in turn can respond via an message

How works To be able to receive a user has to have a mailbox where incoming messages are stored. Each mailbox has a unique address; A user may send an message only if they know the address of the destination mailbox; Privacy: only the owner of the mailbox may examine the content.

How works (cont.) To send an message a user needs an application, for e.g. pine, that allows him to: Compose and edit a message Specify the recipient mailbox. To read a user needs to run some application software, for e.g. pine. Additionally, such an application software, allows a user to: List all the messages in his mailbox; Remove a message from the mailbox; Reply to a message.

Mailbox address format Has two parts separated Prefix: Identifies the user Usually the login name Ex: ungurean Suffix: Domain name of the computer where the mailbox resides; Ex: rbs.rutgers.edu

Client-server paradigm revisited In order for a message to be transmitted, from a sender S to a destination D: A client program,running on S’s machine: Determines the remote machine on which D’s mailbox is stored; Q: how? Uses TCP to send the message across Internet A server program running on D’s machine: Receives the message and stores it into the appropriate mailbox; Sends a notification that the message was received;

Client-server paradigm revisited (cont.) Dealing with failure: the client program keeps a copy of the message for a certain time (usually 3 days); If the client does not receive the notification that the message was received correctly in a certain time, it retransmits the message. When the notification arrives, the client erases the copy. Using from a personal computer: The personal computer does not run an server; Instead, a copy of the mailbox is retrieved from the server, when requested.

The anatomy of an header From: the address (name) of the sender. To: the address of the recipient. CC: list the other recipients (comes from carbon copy) Date: date and time when the message was sent. Subject Attachments: contain the non-text part of the message

Aliases Allow a user to define abbreviations for mailboxes addresses; Can be used instead the mailbox address in the “To” field; Ex: Moreover, there are aliases that are global for a given organization; Ex: help When a user specifies an alias, the software first checks the local list of aliases, and then the global one

Sending to multiple recipients One can send a message to several destinations simply by entering in the To field several addresses (separated by commas); EX: To: Of course, an alias can be used to specify a list of recipients; EX: 375-project=

Other features to and from non-Internet sites; Computers that reside on other networks can still use Idea: there is a computer that links Internet to the other network; Q. What does it mean that a network not belong to the Internet? And did you see this idea before? Where?

Other features (cont.) Access to services via Programs can be written to respond to e- mail messages  Any computer connected to the Internet can provide access to its services via Ex: a computer running database software. Q. What other Internet application can be used for this purpose?

benefits Speed: a message takes only a few seconds to reach the destination Reliable: the message is retransmitted in case of a fault. If a message cannot be delivered, the sender is notified  the most frequently used Internet application.

Some Pine commands Address book Allows you to set an alias for a destination, or a list of destinations Spell Allows you to spell a message before sending it Command Ctrl T Find Allows you to find a message that contains some word Command: Ctrl W