Week 3: E-mail Johan Bollenjbollen/CS312/week3.pdf · 3.E-mail addres is thus not uniquely tied to...
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[email protected] Week 3: E-mail Johan Bollen Old Dominion University Department of Computer Science [email protected] http://www.cs.odu.edu/˜jbollen September 11, 2003 Page 1
Transcript of Week 3: E-mail Johan Bollenjbollen/CS312/week3.pdf · 3.E-mail addres is thus not uniquely tied to...
Week 3:
Johan BollenOld Dominion University
Department of Computer Science
http://www.cs.odu.edu/˜jbollen
September 11, 2003 Page 1
Demo SSHNot always available on windows machines: install and download
http://www.uni-karlsruhe.de/~ig25/ssh-faq/
September 11, 2003 Page 2
1. The internet’s killer-app
(a) Like regular mail (snailmail) butbetter!
i. cheaperii. Quicker
iii. requires little to no overheadiv. Archiving
(b) Probably most popular
i. Enormous volumeii. Lays foundation for myriad
other functionsiii. Oldestiv. Defines internet culture
(c) However!
i. Fraud
ii. The attachment scourge
iii. Security
iv. SPAM
2. Key concepts:
(a) E-mail address and account
(b) SMTP
(c) POP
(d) IMAP
(e) Netiquette
September 11, 2003 Page 4
User IDs, Passwords and E-mail addresses
1. User IDs and accounts
(a) Context is UNIX system
(b) Each user has unique ID andaccount on system
(c) typically:
i. initial of first nameii. last name
iii. 8 characters
2. Passwords
(a) Account access is restricted to
user
(b) Use of passwords
(c) Security considerations
September 11, 2003 Page 5
E-mail addresses
1. Natural consequence of UNIX accountand user ID management
(a) user ID + host identify user
(b) use of@ to combine both
(c) host is identified by hostname (notIP?)
(a) user ID =jbollen
(b) hostname =cs.odu.edu
(c) combined=e-mail address
3. E-mail addres is thus not uniquely tied
to individual
(a) Many possible hosts
(b) Many possible user names
(c) None need to reflect identity of
user
4. Determine someone’s adddress?
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Writing an e-mail
1. To: field
2. Cc: field
3. Bcc: field
4. Attachments
5. Body:
(a) Netiquette
i. Salutationii. Spelling?
iii. Appropriate languageiv. NO SHOUTING
(b) Keep in mind who will receive
(c) Treat as business mail
(d) Emotionally charged e-mails
i. Lack of body language is
dangerous
ii. 10 minute rule
iii. Never attribute to malice that
which...
6. Signature
(a) Most e-mail clients have specific
setting
(b) Keep it concise
(c) Be a minimalist
7. Forwarding
(a) Message
(b) To other accounts: .forward
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Attachments
1. File is attached to e-mail
(a) Receiver can save to local system
(b) Convenient way to share files
2. Not part of original intent
(a) Attachment is sent as part ofmessage
(b) Convert original file to textrepresentation
3. I recommend against attachments
(a) Burden on slow connections (mail
bomb)
(b) Security risk
(c) Often unnecessary!
(d) Requires applications to decode
and display
(e) Alternative: send URL
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E-mail inner workings
1. Post system
(a) Origin
(b) Destination
(c) Delivery
2. Internet:
(a) Computers are intermediaries
(b) user→computer→computer→user
(c) Actual system:
i. Mail clients
ii. Mail servers
iii. Mail accounts
iv. SMTP/POP protocols
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Simple Mail Transfer Protocol
1. Set e-mail on its path
2. Client and mail server handshake and
communicate
3. Simple command set communicated
on port 25 of mail server:
(a) HELO domain.name
(b) MAIL FROM: your @address
(c) RCPT TO: yourfriend
(d) DATA
(e) Terminate with . and enter
(f) QUIT
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Post Office Procol
1. Used to retrieve e-mail from mailserver to local host
2. Client and mail server handshake andcommunicate on port 110
3. Set of commands to retrieve e-mails
(a) USER yourlogin
(b) PASS pasword
(c) STAT
(d) LIST
(e) RETR number
(f) DELE number
(g) QUIT
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Some notes on SMTP and POP
1. No security
(a) Passwords and logins transferedunprotected
(b) SMTP does not requireauthentication
(c) SPAM heaven!
2. SMTP + POP
(a) Standard configuration:
i. Load e-mail to local hostii. Remove from mail server
iii. E-mail no longer accessiblefrom anywhere
iv. No backups
(b) Other possibilities
i. Telnet to mailserver
ii. Read e-mail using PINE
iii. Always accessible given telnet
+ internet
(c) IMAP
3. Mailserver problems
(a) Does not exist or defunct:
bounced mail
(b) Need to be reliable systems
(c) Sufficient space?
(d) Other than that: anyone can run
mailserver
September 11, 2003 Page 14
IMAP explained
1. Internet Message Access Protocol
2. Intended to solve POP’s problems
(a) POP is simple
(b) download e-mail and delete
(c) or leave in place
(d) Synchronization problemsbetween several systems
3. IMAP
(a) RFC:http://www.isi.edu/in-notes/rfc3501.txt
(b) Leave messages on server
(c) Only download those you want toread
(d) Folder management on server and
client
4. Comparison
(a) POP: periodic contact, IMAP
continous
(b) IMAP Mail remains on server
(c) Folders, address books, etc are
centralized on server
5. Compatibility
(a) PINE
(b) Outlook express
(c) Netscape
(d) Eudora
(e) Ximian
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Where do e-mails go?
Shortly: to your accounts mail spool
1. disk space allocated for e-mails
2. accessible through POP
3. /var/mail/jbollen
4. Flat ASCII file structure
(a) parsing is done by POP or locale-mail client
(b) Attachments? go there too:encoded BASE64 + Mineheaders
i. Content-typeii. Content-Transfer-Encoding
iii. boundary delimiters
(c) see:http://bcn.boulder.co.us/~neal/attachments.html
September 11, 2003 Page 17
E-mail filtering
One big inbox?
1. hundreds of messages can accumulate
2. need to organize
(a) not part of e-mail protocols
(b) mail spool is simple flat text file
(c) Responsibility of client
3. Most e-mail clients can filter e-mail
(a) Define set of filter rules on To:,
From, etc fields
(b) Depending on match, move
message to separate folder
4. procmail
(a) UNIX tool
(b) independent from client
(c) use script file: RE and actions
September 11, 2003 Page 18
Mailing lists
1. E-mail is essentially a point-to-pointsystem
(a) Communication between twoindividuals
(b) Set up to simulate regular mail
2. Need to broadcast messages
(a) Group discussion
(b) Announcements
3. Mailing lists
(a) Managed by list owner
(b) Subscription based
(c) Messages are broadcast via
mailing list server
(d) Always check cc:!!!
September 11, 2003 Page 19
