Page 187 - DCAP516_COMPUTER_SECURITY

Unit 14: Intrusion Detection System and Secure E-mail

Advanced Features Notes

1. Automatical forwarding
2. Automatical reply
3. Mailboxs
4. Distribution list

5. Registered mail
6. Others: carbon copies, high-priority mail, secret (encrypted) mail, alternative recipients,
etc.

A key idea in all modern e-mail systems is the distinction between the envelope and its contents.

14.6.2 Architecture and Services

An email system normally consists of two subsystems:
1. User agents: which allow people to read and send email.
2. Message transfer agents: which move the messages from the source to the destination.

The User Agent

The user agent is normally a program (e.g., a mail reader) that accepts a variety of commands
that relate to composing, sending, and receiving messages and manipulating mailboxes.

Sending email

To send an email, a user must provide the message, the destination address (normally in DNS
format), and possibly some other parameters (e.g., the priority or security level).

Most email system support mailing lists, so that a user can send the same message to a list of
people with a single command.

Reading email

The user agent program typically starts with looking at the user’s mailbox for incoming mail
before displaying anything on the screen. Then it will announce the number of messages in the
mailbox and wait for a command, as illustrated in Figure 14.3:

Figure 14.3: Sample Inbox Format

# Flags Bytes Sender Subject
1 K 1030 asw Changes to MINIX
2 KA 6348 trudy Not all Trudys are nasty
3 K F 4519 Amy N. Wong Request for information
4 1236 bal Bioinformatics
5 104110 kaashoek Material on peer-to-peer
6 1223 Frank Re: Will you review a grant proposal
7 3110 gukio Our paper has been accepted
8 1204 dmr Re: My student’s visit

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