Electronic mails (Emails)

1. Electronic mails (Emails) CSC1720 – Introduction to Internet Essential Materials

2. Outline • Part I – General part • Email basics • How does email work? • Basic email operations • Signatures, Attachment (MIME) • Part II – Technical part • SMTP, HTTP, POP and IMAP • Part III – more advanced • SPAM & CAUCE • Email etiquette (Netiquette) • CUHK CWEM & Phonebook directory All copyrights reserved by C.C. Cheung 2003.

3. What is Email? • A mail, but is sent electronically across the Internet. • Quickly delivered in seconds or minutes (if without problem). All copyrights reserved by C.C. Cheung 2003.

4. Pros & Cons • Advantages • Convenience, Fast speed, Inexpensive, Printable, Reliable, Global, Generality (not limited to text, but graphics, programs, even sounds) • Disadvantages • Misdirection, Interception, Forgery, overload, Funk (Spamming), No response (from the receiver). • Think one good and one bad experience that you have had with email. All copyrights reserved by C.C. Cheung 2003.

5. The growth of Email Users & Messages • Figure from "Discovering 2000", Shelly Cashman Series, Thomson Learning All copyrights reserved by C.C. Cheung 2003.

6. Email address • What you need is • The E-mail address of the recipient. • user@host • cccheung@cse.cuhk.edu.hk • eng70132@leonis.nus.sg • "cse.cuhk.edu.hk" is the domain name of the mail server which handles the recipient's mail. • “cccheung" is the user name of the recipient. • User name and hostname are separated by "@". All copyrights reserved by C.C. Cheung 2003.

7. Email server and client • Email client– software / program that can transfer e-mail from a local host to a local e-mail server. • Email server– software/program that can send/receive e-mail from/to other email servers. • Mailbox– An electronic mailbox is a disk file which holds email messages. All copyrights reserved by C.C. Cheung 2003.

8. Electronic mailbox All copyrights reserved by C.C. Cheung 2003.

9. Email Software (Client) • Graphical Client (User friendly) • OutlookNetscape All copyrights reserved by C.C. Cheung 2003.

10. Email Software (Client) • Text mode (UNIX - mailserv, logic server) • muttpine All copyrights reserved by C.C. Cheung 2003.

11. Email Software (Server) • Install the mail server on Linux/Unix or Windows platform. All copyrights reserved by C.C. Cheung 2003.

12. Signature Header Greeting Text Signature All copyrights reserved by C.C. Cheung 2003.

13. Cc & Bcc • Carbon Copy Section • Send a message to more than one person, all the recipients will see the list of email addresses. • Blind Carbon Copy Section • The addresses won’t be seen by the recipients. • When email is sent to a large group of people who don’t know each other. All copyrights reserved by C.C. Cheung 2003.

14. Attachment – MIMEMulti-purpose Internet Mail Extension • A protocol for transmitting non-text information across the Internet. Basically, non-ASCII data is converted to ASCII for transmission and then converted back at the receiver. • A specification for automatically sending objects other than text in email messages. • MIME is usually associated with multimedia, such as images, audio recordings, and movies. • Additional hardware and helper software are usually required. • Common MIME-compliant mailers: • pine, metamail, Netscape messenger, MS Outlook All copyrights reserved by C.C. Cheung 2003.

15. ASCII Code Examples of the ASCII encoding Consists of fixed length codes of 7-bits (0 or 1) All copyrights reserved by C.C. Cheung 2003.

16. EncodingASCII & Double-byte All copyrights reserved by C.C. Cheung 2003.

17. MIME All copyrights reserved by C.C. Cheung 2003.

18. Common MIME Types All copyrights reserved by C.C. Cheung 2003.

19. MIME headers • MIME-Version: 1.0 • Content-type: multipart/mixed: boundary=“simple boundary” • --simple boundary • …… • --simple boundary • …… • --simple boundary-- All copyrights reserved by C.C. Cheung 2003.

20. MIME Example All copyrights reserved by C.C. Cheung 2003.

21. How does email works? All copyrights reserved by C.C. Cheung 2003.

22. SMTP • E-mails are transferred across the Internet via Simple Mail Transfer Protocol (SMTP). • The mail server uses SMTP to determine how to route the message through the Internet and then sends the message. • When the message arrives at the recipient's mail server, the message is transferred to a POP3 server. POP stands for Post Office Protocol. • The POP server holds the message until the recipient retrieves it with his/her email software. All copyrights reserved by C.C. Cheung 2003.

23. Mary’s computer John’s computer Internet SMTP SMTP SMTP Mail server Mail server SMTP illustration All copyrights reserved by C.C. Cheung 2003.

24. POP • Advantages • Don’t have to know the name of your machine • POP mail server is installed on a computer always ON • Use Windows interface to read email • Disadvantages • The email at the mail server is popped to your local machine • Refer to notes page for more explanations All copyrights reserved by C.C. Cheung 2003.

25. Mary’s computer John’s computer Local inbox Internet POP SMTP SMTP SMTP Mail spool Mail server Mail server POP illustration All copyrights reserved by C.C. Cheung 2003.

26. How to setup email client in Netscape? Select POP server Select SMTP server All copyrights reserved by C.C. Cheung 2003.

27. IMAP • Another popular method by which users obtain their emails is called a central mail spool. • Imagine what could happen if Peter where reading emails at his office while his wife was simultaneously trying to read from the same inbox from home. • Lots of complication can arise in this scenario, and a protocol has been designed to handle many of the relevant issues. It's called the Interactive Mail Access Protocol (IMAP). • Peter's emails remain on his mail server. The emails are not brought over to the computer from which he is working. That is, leaving the emails in a central location, and allowing access of the emails from several places. • That is, when Peter wants to read his emails, he must send a password to the mail server to authenticate himself. • Another advantage of IMAP is that it encrypts passwords so that someone sniffing the network cannot directly obtain his password. All copyrights reserved by C.C. Cheung 2003.

28. John’s office computer John’s home computer IMAP link IMAP link Incoming/ Outgoing emails John inbox Mail server (SMTP/IMAP) IMAP illustration All copyrights reserved by C.C. Cheung 2003.

29. How to setup IMAP in Outlook Express? Select the correct Protocol POP email HTTP email IMAP email All copyrights reserved by C.C. Cheung 2003.

30. Web-based e-mail - HTTP • Can deliver mail message in web page format. • More reliable to use POP and IMAP than HTTP mail account. All copyrights reserved by C.C. Cheung 2003.

31. Bounced back email • Bad user account name • Bad domain name • Domain name server is down for several days • Some other malfunction (email too big) All copyrights reserved by C.C. Cheung 2003.

32. Email Virus - Melissa • May 24, 1999, Melissa virus is spreading as RTF files. • 300 organizations affected, 100,000 hosts. • One site reported, 32,000 copies of email are received in 45 minutes. • Not a worm, require user interaction to propagate the virus. • Why called Melissa? • Named by the antivirus software vendors. • Don’t open attachment  not infected. All copyrights reserved by C.C. Cheung 2003.

33. Junk Mails • How can they get into your mailbox? • From name card, letter heads, published papers. • Use search engine in the newsgroup, bulletin boards, phone books. • Dump a full user list in a server. • How to stop the intrusion of Junk Mails? • Mail server providers joint effort • Filtering • Preview before downloading All copyrights reserved by C.C. Cheung 2003.

34. SPAM • SPAM is flooding the Internet with many copies of the same message • Force to send message to people • Junk electronic mail. • Why cause problem? • Cost-shifting – very cheap to send thousands of emails • Fraud – not an advertisement subject • Waste of others’ resources – stealing bandwidth • Displacement of Normal Email – destroy the usefulness and effectiveness of email • Ethics problem All copyrights reserved by C.C. Cheung 2003.

35. Anti - SPAM All copyrights reserved by C.C. Cheung 2003.

36. CAUCE - Coalition Against Unsolicited Commercial E-mail • An all volunteer organization which is created by Netizens over the world. All copyrights reserved by C.C. Cheung 2003.

37. CUHK CWEMCampus Wide Email System • Provided by the Computer Services Center (CSC). • The system resides in mailserv.cuhk.edu.hk • which is a Sun Ultra-Enterprise 2 Model 2200 Server. • Every student is given an email account and mailbox with 2 megabytes storage space. • Computing id / login name / username: • Your computing id is an "s" plus first 6 digits of the student id number. • Computing id for s00201960 is s002019 • E-mail address: • your-computing-id@mailserv.cuhk.edu.hk, • your-alias@cuhk.edu.hk • s002019@mailserv.cuhk.edu.hk stevenchan@cuhk.edu.hk All copyrights reserved by C.C. Cheung 2003.

38. CUHK – Phonebook directory • Works together with CWEM • Provide you: • an easy-to-remember email address (alias) • a means to enquire email address of all staffs and students (query) • a means to redirect emails (forward) • Try the phonebook All copyrights reserved by C.C. Cheung 2003.

39. References • Discussion – handouts • SPAM & Chinese DNS • Internet FAQ Archives • How USENET protocol works? • http://email.about.com/ • The End. • Thank you for your patience! All copyrights reserved by C.C. Cheung 2003.