CSC 140: Introduction to IT

CIT 140: Introduction to IT Slide #1

CSC 140: Introduction to IT

Electronic Mail


Topics

• What is E-mail?

• E-mail Protocols

• E-mail Addresses

• E-mail Headers

• UNIX e-mail Applications

– mail

– pine

– KMail


What is E-mail?

A method of composing, sending, and receiving messages over electronic communication systems.


E-mail Transfer Dialog


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.


Example SMTP SessionS: 220 www.example.com ESMTP Postfix C: HELO mydomain.com S: 250 Hello mydomain.com C: MAIL FROM: <[email protected]> S: 250 Ok C: RCPT TO: <[email protected]> S: 250 Ok C: DATA S: 354 End data with .C: Subject: test message C: From: [email protected] C: To: [email protected] C: C: Hello, C: This is a test. C: . S: 250 Ok: queued as 12345 C: QUIT S: 221 Bye


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.


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 [email protected] addresses.

mailto:[email protected]


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.


E-mail [email protected]

– 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.


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.


Example E-mail HeadersFrom [email protected] 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 <[email protected]>; 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: [email protected] (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: <[email protected]>Date: Thu, 15 Sep 2005 03:05:55 -0500Reply-To: Bruce Xyzzy <[email protected]>From: Bruce Xyzzy <[email protected]>Subject: CRYPTO-GRAM, September 15, 2005To: [email protected]: list


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


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--


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.


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.


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.


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.


E-mail Features


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


Graphical E-mail with KMail


pine


Composing E-mail with pine


Using the pine Address Book

CSC 140: Introduction to IT

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