Page 190 - DCAP516_COMPUTER_SECURITY

Computer Security

Notes However mail gateways have an advantage providing interoperability i.e. they provide
connections among standard TCP/IP mail systems and other mail systems as well as between
TCP/IP Internets and networks that do not support Internet protocols. So when there is a change
in protocol then the mail gateway helps in translating the mail message from one protocol to
another since it will be designed to understand both.

Notes Email using SMTP works best when both the sender and the receiver are on the
Internet and can support TCP connections between sender and receiver.

Email gateways are needed to enable email exchanges between Internet machines and
non-Internet machines.

Problems

1. Different addresses.
2. Different envelope or header fields.

3. Incompatible email body: e.g.
What should a gateway do with a message from the Internet whose body holds a reference to an
audio file to be obtained by FTP if the destination system does not support this concept?

Final Delivery

What to receive emails from an email server when a user has no capability of sending/receiving
emails directly?
POP3 (Post Office Protocol) is an ASCII protocol that is used for fetching email from a remote
mailbox. It has commands for the user to log in/out, fetch messages, and delete messages.

IMAP (Interactive Mail Access Protocol) was designed to help the user who uses multiple
computers to access emails from the email server (a central repository that can be accessed from
any machine).
DMSP (Distributed Mail System Protocol is part of the PCMAIL. It allows users to download
email from the server to any machine.
Filter tools can be used to check incoming emails and take specified actions.
Vacation daemon program can be used to each incoming email and sends the sender an insipid
reply.
Self Assessment

State whether the following statements are true or false:
7. The protocol used by the MTA ‘s on the source and destination side is called SMTP.
8. An email system normally consists of five subsystems.
9. Example of symmetric PGP is RSA.

10. Mail gateways are also called mail relays, mail bridges and are introducing unreliability.
11. Email gateways are needed to enable email exchanges between Internet machines and
non-Internet machines.

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