1. E-Mail Security E-Mail Technology E-Mail Clients and Mail Servers
Mail server software: Sendmail on UNIX, Microsoft Exchange, and Lotus/IBM

2. E-Mail Standards SMTP to Send POP or IMAP to Download SMTP to Send
Sender’s
Mail Server
Receiver’s
Mail Server
Sending
Client
Receiving
Client
Message
RFC 822 or 2822 body
HTML body

3. E-Mail Security E-Mail Technology
SMTP to send messages from client to mail server or from mail server to mail server
To download messages to client program from receiver’s mail server
POP: Simple and popular; manage mail on client PC
IMAP: Can manage messages on mail server

4. E-Mail Security E-Mail Technology E-mail bodies
RFC 822 / RFC 2822: Plain English text
HTML bodies: Graphics, fonts, etc.
HTML bodies might contain scripts, which might execute automatically when user opens the message
Web-based needs only a browser on the client PC

5. No need to install new software
Web-Based
Client’s
Browser
Webserver
Program
HTTP Request Message
HTTP Response Message
Webpage
Containing
Message
Client PC
Webserver with
Web-Based
Almost all client PCs
now have browsers.
No need to install new software

6. E-Mail Security E-Mail Content Filtering
Antivirus filtering and filtering for other executable code
Especially dangerous because of scripts in HTML bodies
Spam: Unsolicited commercial

7. E-Mail Security E-Mail Content Filtering
Volume is growing rapidly: Slowing and annoying users (porno and fraud)
Filtering for spam also rejects some legitimate messages
Sometimes employees attack spammers back; only hurts spoofed sender and the company could be sued

8. E-Mail Security Inappropriate Content
Companies often filter for sexually or racially harassing messages
Could be sued for not doing so

9. E-Mail Security E-Mail Retention
On hard disk and tape for some period of time
Benefit: Can find information
Drawback: Can be discovered in legal contests; could be embarrassing
Must retain some messages for legal purposes

10. E-Mail Security E-Mail Retention
Shredding on receiver’s computer to take messages back
Send key to decrypt
Make key useless after retention period so cannot retrieve anymore
Might be able to copy or print before retention limit date
Not good for contracts because receiver must be able to keep a copy

11. E-Mail Security E-Mail Retention
Message authentication to prevent spoofed sender addresses
Employee training
is not private; company has right to read
Your messages may be forwarded without permission
Never put anything in a message they would not want to see in court, printed in the newspapers, or read by their boss
Never forward messages without permission

12. E-Mail Security E-Mail Encryption
Not widely used because of lack of clear standards
PGP and S/MIME for end-to-end encryption
How to get public keys of true parties?
PGP uses trust among circles of friends: If A trusts B, and B trusts C, A may trust C’s list of public keys
S/MIME requires expensive and cumbersome PKI

13. Cryptographic Protection for E-Mail
Mail Server
SMTP, POP, etc.
Over TLS
SMTP, POP, etc.
over TLS
S/MIME with PKI or
PGP with Circles of Trust
Sending
Client
Receiving
Client

14. E-Mail Security E-Mail Encryption
PGP and S/MIME for end-to-end encryption
Ease of use
S/MIME usually built in if available at all
PGP usually a cumbersome add-on to
TLS
Between client and server