Email Service

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Email Service
2
Outline

• Mail Reader and Mail Server
• Mail Message Format
• Mail Protocols
• Sample MIME messages
• Practices
• References

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Mail Reader and Mail Server

• Mail Reader
• Email program that allows a user t create, edit,
  store and forward e-mail messages
• Mail Reader is also called UA (User Agent)
• Such as Outlook Express, Netscape Composer, ping,
  elm
• Mail Server
• A program (aka a daemon or a server) that in
  charge of storing and forwarding e-mail messages
• Mail Server is also called MTA (Mail Transfer
  Agent), function like postman and post-office.
• Such as sendmail, qmail, Microsoft Exchange

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Mail Message Format (RFC 2822)
Header
A blank line
Body

• A mail message consists of a header followed,
  optionally, by a body.
• Header fields (see example above) contains From
  , To , Subject, Date ...etc.
• Body contains what user wants to say (including
  nontext-based information, such as html, image,
  or attached files).

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Mail Message Format (RFC 2822)

• RFC 822 headers

• RFC 822 headers added by MIME

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Mail Protocols

• SMTP (Simple Mail Transfer Protocol) 25
• An internet protocol for sending (transferring)
  e-mail
• Both Mail reader and Mail Server (daemons) speak
  SMTP to transfer e-mail, the mail server accepts
  connection on port 25 and copies mail messages
  into appropriate mailboxes.
• POP3 (110), IMAP (143)
• POP/IMAP allow mail reader to receive e-mail
  messages.
• POP3 stands for Post Office Protocol version 3
• IMAP stands for Internet Message Access Protocol
• Both support offline reading (download to PC)
• IMAP allow user to create and manipulate folders
  and mailboxes and more functionalities.

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Mail Protocols

• MIME (Multipurpose Internet Mail Extensions) RFC
  1341
• MIME add structure to the message header and body
  and defining encoding rules for non-ASCII
  messages.
• With MIME, we can send multimedia mail message,
  including html mail, image, Rich Text Format
  document (RTF), and attached files and in
  different languages (such as Chinese, Japanese,
  Hebrew).

• RFC 822 headers added by MIME

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Mail Protocols

• The MIME content types and subtypes defined in
  RFC2045, 2046.

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Mail Protocols

• The MIME content transfer encoding (tells how
  the body is wrapped for transmission), currently
  there are five schemes provided to encode
  non-ASCII material

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Sample MIME messages

• From James Bondltexample_at_example.comgtTo Indiana
  Jones
• Subject Hello from 007
• MIME-Version 1.0
• Content-Type multipart/mixed
• boundary"XXXXboundary text"
• --XXXXboundary text
• Content-Type text/plain
• this is the body text
• --XXXXboundary text
• Content-Type text/plain
• Content-Disposition attachment
• filename"test.txt"
• this is the attachment text
• --XXXXboundary text--

Header
A blank line
1st body part
Body
2nd body part
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Sample MIME message

• A text/html MIME mail message with pictures.

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Header
1st body part(text/html)
2nd body part(image/gif)
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Practices

• Installing a Mail Server (Winmail is suggested)
• Sending Email via Telnet
• Receiving Email using Mail Reader
• Setting up
• Inside out the Message format
• Monitoring the interaction of mail client and
  server using sockspy
• Receiving Email via telnet (POP3)
• Sending a Simple HTML mail
• Sending a multimedia mail (html, image and
  attachments, refer to reference for online base64
  encoding)
• Writing a simple mail client using Tcl, PHP or...
  (better have SMTP Authentication support, hint
  AUTH LOGIN and Tcllib base64 package)

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References

• Computer Networks 4th Edition Chap7.2, Andrew S.
  Tanenbaum, Prentice Hall, 2003/03
• online base64 encoding
• http//www.motobit.com/util/base64-decoder-encoder
  .asp
• Sending e-mail via Telnet
• http//www.activexperts.com/activemail/telnet/
• How to send an e-mail with attached file
• http//www.hochfeiler.it/alvise/smtp.htm
• Telnet POP3 Tutorial
• http//manual.liquidweb.com/chapter3/pop3.htm
• SMTP Auth Email Script (PHP)
• http//codewalkers.com/getcode.php?id538