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CIT 140: Introduction to IT Slide #1
CSC 140: Introduction to IT
Electronic Mail
CIT 140: Introduction to IT Slide #2
Topics
• What is E-mail?
• E-mail Protocols
• E-mail Addresses
• E-mail Headers
• UNIX e-mail Applications
– pine
– KMail
CIT 140: Introduction to IT Slide #3
What is E-mail?
A method of composing, sending, and receiving messages over electronic communication systems.
CIT 140: Introduction to IT Slide #4
E-mail Transfer Dialog
CIT 140: Introduction to IT Slide #5
E-mail Protocols: Sending
Simple Mail Transfer Protocol (SMTP)– This dictates the format of the message in terms
of an envelope, a header and a body and facilitates the movement of the message between the components of a typical e-mail transfer.
Domain Name System (DNS)– This dictates the exact form of an e-mail
address.
CIT 140: Introduction to IT Slide #6
Example SMTP SessionS: 220 www.example.com ESMTP Postfix C: HELO mydomain.com S: 250 Hello mydomain.com C: MAIL FROM: <sender@mydomain.com> S: 250 Ok C: RCPT TO: <friend@example.com> S: 250 Ok C: DATA S: 354 End data with .C: Subject: test message C: From: sender@mydomain.com C: To: friend@example.com C: C: Hello, C: This is a test. C: . S: 250 Ok: queued as 12345 C: QUIT S: 221 Bye
CIT 140: Introduction to IT Slide #7
E-mail Protocols: Receiving
Post Office Protocol (POP) or Internet Message Access Protocol (IMAP)– Works best for offline e-mail reading from a
single host computer that contains your e-mail.
Multipurpose Internet Mail Extensions (MIME)– This dictates the format of multimedia files
used as attachments to an e-mail message.
CIT 140: Introduction to IT Slide #8
History of E-mail1965
– First e-mail on mainframe systems like CTSS.
1969– Internet started.– First e-mail messages sent on Internet.
1978– First spam e-mail message sent from a DEC engineer.
1981– RFC 788 published, describing SMTP.
1983– DNS released, allowing user@host.domain addresses.
CIT 140: Introduction to IT Slide #9
E-mail Addresses
Bang Paths– utzoo!decvax!harpo!eagle!mhtsa!ihnss!ihuxp!grg
– Recipient: grg
– Recipient’s machine: ihuxp
– Machines connected by modems at night to avoid long-distance charges.
– Transmission times measured in days.
CIT 140: Introduction to IT Slide #10
E-mail Addressesjw@cs.nku.edu
– Top level domain: edu• Limited: com, edu, gov, net, org, country codes• Internet Assigned Numbers Authority (IANA)• ICANN controls IANA
– Subdomain: nku• Allocated by top-level domain administrators.
– Hostname: cs• Allocated by subdomain administrators.
– Username: jw• Allocated by hostname administrators.
CIT 140: Introduction to IT Slide #11
E-mail Headers
To: contains e-mail address(es) of recipient(s)
From: contains the e-mail address of sender.
Cc: address(es) of additional recipient(s).
Date: Date and time at which message was sent.
Attch: lists any attachments that might accompany the message, usually in the form of external files.
Subject: indicates the subject of message.
Received: tracking information indicating which servers handled the message.
CIT 140: Introduction to IT Slide #12
Example E-mail HeadersFrom owner-crypto-list@LISTSERV.MODWEST.COM Thu Sep 15 06:03:01 2005Received: from mailapp0.msomt.modwest.com (mailapp0.msomt.modwest.com
[216.220.25.71]) by smtp.utoledo.edu (8.14.7) with ESMTP id j8FA30407908 for <zeecat@utoledo.edu>; Thu, 15 Sep 2005 06:03:00 -0400 (EDT)
Received: from nat.dd-b.net (HELO rafael) (61.221.11.71) by mpls-pop-13.inet.qwest.net with SMTP; 15 Sep 2005 08:06:00 -0000X-Sender: schneier@counterpane.com (Unverified)X-Mailer: QUALCOMM Windows Eudora Pro Version 4.2.2Mime-Version: 1.0Content-Type: text/plain; charset="us-ascii"; format=flowedX-Modwest-MailScanner: Found to be cleanMessage-ID: <4.2.2.20050915030222.02c6ea30@61.221.11.71>Date: Thu, 15 Sep 2005 03:05:55 -0500Reply-To: Bruce Xyzzy <xyzzy@COUNTERPANE.COM>From: Bruce Xyzzy <xyzzy@COUNTERPANE.COM>Subject: CRYPTO-GRAM, September 15, 2005To: CRYPTO-GRAM-LIST@LISTSERV.MODWEST.COMPrecedence: list
CIT 140: Introduction to IT Slide #13
Attachments• E-mail historically used 7-bit ASCII.• Binary files, such as images or programs,
require 8 bits of data per byte.• MIME
– Encodes 8-bit files as 7-bit ASCII.– Stores multiple files with a single message.
• MIME Headers– MIME-Version: 1.0 – Content-type: text/plain– Content-transfer-encoding: base64
CIT 140: Introduction to IT Slide #14
MIME Message ExampleContent-type: multipart/mixed; boundary="frontier" MIME-version: 1.0 --frontier Content-type: text/plain This is the body of the message. --frontier Content-type: application/octet-stream Content-transfer-encoding: base64
gajwO4+n2Fy4FV3V7zD9awd7uG8/TITP/vIocxXnnf/5mjgQjcipBUL1b3uyLwAVtBLOP4nV LdIAhSzlZnyLAF8na0n7g6OSeej7aqIl3NIXCfxDsPsY6NQjSvV77j4hWEjlF/aglS6ghfju FgRr+OX8QZMI1OmR4rUJUS7xgoknalqj3HJvaOpeb3CFlNI9VGZYz6H6zuQBOWZzNB8glwpC
--frontier--
CIT 140: Introduction to IT Slide #15
PrivacyE-mail is transmitted through several MTAson its way from sender to recipient.
– E-mail can be read on disk of mail server.– E-mail can be read in transit using a sniffer.
Additional privacy issues– Your e-mail address is included in headers.– Your e-mail server is displayed in headers.
CIT 140: Introduction to IT Slide #16
ThreatsSnooping
– Others reading your e-mail.Spoofing
– Forging e-mail to appear to be from someone else.Identity Theft
– An attacker impersonates you or someone you know by spoofing e-mail to appear to be from them.
– PhishingRepudiation
– Since attackers can impersonate others in e-mail, people deny sending e-mail they actually wrote.
Fraud– 419 scams.
CIT 140: Introduction to IT Slide #17
Security Measures
Encrypt e-mail in transit.– SSL encryption for POP, IMAP, SMTP.– Many e-mail clients and servers support.– Also SSL encryption for webmail.
Encrypt e-mail before transit– PGP and S/MIME (incompatible with each other.)– Must exchange cryptographic keys with recipient.– E-mail encrypted in storage and in transit.– Message Authentication Codes used to check if
encrypted message was altered.
CIT 140: Introduction to IT Slide #18
UNIX E-mail Files
/var/mail/username/var/spool/mail/username
– A user’s e-mail messages.
/var/spool/mqueue– Messages queued for sending to other hosts.
/etc/mail– Mail server (MTA) configuration files.
/etc/mail/aliases– MTA mailing lists.
CIT 140: Introduction to IT Slide #19
E-mail Features
CIT 140: Introduction to IT Slide #20
The UNIX mail Command
Options for sending e-mail with the mail command-s A subject: line is included in the message
header
for all recipients
-c A carbon copy is sent to address add
-b A blind carbon copy is sent to address add
-h A screen display of message headers is shown
first
-p All messages are displayed with full headers
CIT 140: Introduction to IT Slide #21
Graphical E-mail with KMail
CIT 140: Introduction to IT Slide #22
Graphical E-mail with KMail
CIT 140: Introduction to IT Slide #23
Graphical E-mail with KMail
CIT 140: Introduction to IT Slide #24
Graphical E-mail with KMail
CIT 140: Introduction to IT Slide #25
Graphical E-mail with KMail
CIT 140: Introduction to IT Slide #26
pine
CIT 140: Introduction to IT Slide #27
Composing E-mail with pine
CIT 140: Introduction to IT Slide #28
Using the pine Address Book