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COS 420

COS 420. DAY 25. Agenda. Assignment 5 posted Chap 22-26 Due May 4 Final exam will be take home and handed out May 4 and Due May 10 Today we will discuss Electronic Mail (SMTP, POP, IMAP, MIME). Project 2 Grading. Meeting Timelines 10% Deliverables

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COS 420

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  1. COS 420 DAY 25

  2. Agenda • Assignment 5 posted • Chap 22-26 • Due May 4 • Final exam will be take home and handed out May 4 and Due May 10 • Today we will discuss Electronic Mail (SMTP, POP, IMAP, MIME)

  3. Project 2 Grading • Meeting Timelines 10% • Deliverables • Program requirements Due March 30 15% • late • Protocol Definition Due April 13 15% • Better but I hope to see improvement by May1 • Working Network Application Due May 4 25% • Final Paper Due May 1 25% • User Manual • Protocol • Program requirements • Technical Specifications • Presentation Due May 4 10%

  4. Electronic Mail • Among most widely used Internet services • Two major components • User interface • Mail transfer software • Paradigm: transfer is separate background activity

  5. Illustration Of Email System Components

  6. Mailbox Names And Aliases • Email destination identified by pair ( mailbox, computer ) • Aliases permitted (user enters alias that is expanded)

  7. Forwarding • Powerful idea • Email arriving on a computer can be forwarded to an ultimate destination

  8. Illustration Of Aliases And Forwarding

  9. TCP/IP Standards For Email • Syntax for email addresses • Format of email message • Protocols for email transfer and mailbox access

  10. Email Address Syntax • Mailbox identified by string mailbox@computer • String computer is domain name of computer on which a mailbox resides • String mailbox is unique mailbox name on the destination computer

  11. Format Of Email Message • Message consists of • Header • Blank line • Body of message • Headers have form keyword : information • Standard given in RFC 2822

  12. E-mail header Return-Path: <voisine@maine.edu> Received: from granite.unet.maine.edu ([unix socket]) by granite.unet.maine.edu (Cyrus v2.2.12-Maine-RPM-2.2.12-3.RHEL4.1.um.2) with LMTPA; Fri, 28 Apr 2006 14:16:12 -0400 X-Sieve: CMU Sieve 2.2 Received: from VoisineScott (VoisineScott.umfk.maine.edu [130.111.68.129]) by granite.unet.maine.edu (8.13.1/8.13.1) with ESMTP id k3SIEdHh000307; Fri, 28 Apr 2006 14:15:06 -0400 From: "Scott Voisine" <voisine@maine.edu> To: "Scott Voisine" <voisine@maine.edu> Subject: EDU 405 Play Date: Fri, 28 Apr 2006 14:14:39 -0400 Message-ID: <003101c66aef$a9e2f830$81446f82@NETUMFK.EDU> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0032_01C66ACE.22D15830" X-Mailer: Microsoft Office Outlook 11 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2869 Thread-index: AcZq75BMY/2KYcRVRGurpMOPNTltNA== X-MailScanner-Information: Please contact the ISP for more information X-MailScanner: Found to be clean X-MailScanner-From: voisine@maine.edu

  13. Protocol For Email Transfer • Specifies interaction between transfer components • Transfer client • Transfer server • Standard protocol is Simple Mail Transfer Protocol (SMTP)

  14. SMTP • Application-level protocol • Uses TCP • Commands and responses encoded in ASCII

  15. Example Of SMTP

  16. Protocol For Mailbox Access • Used when user’s mailbox resides on remote computer • Especially helpful when user’s local computer is not always on-line • Two protocols exist • Post Office Protocol version 3 (POP3) • Internet Message Access Protocol (IMAP) • Each provides same basic functionality • User authentication • Mailbox access commands

  17. Multipurpose Internet Mail Extensions (MIME) • Permits nontextual data to be sent in email • Graphics image • Voice or video clip • Sender • Encodes binary item into printable characters • Places in email message for transfer • Receiver • Receives email message containing encoded item • Decodes message to extract original binary value

  18. MIME Header • Header in email message describes encoding used • Example From: bill@acollege.edu To: john@example.com MIME-Version: 1.0 Content-Type: image/jpeg Content-Transfer-Encoding: base64 ...data for the image...

  19. Seven Basic MIME Types

  20. Example Of Mixed / Multipart Message

  21. Summary • Email operates at application layer • Conceptual separation between • User interface • Mail transfer components • Simple Mail Transfer Protocol (SMTP) • Standard for transfer • Uses ASCII encoding • Post Office Protocol (POP) And Internet Mail Access Protocol (IMAP) allow access of remote mailbox. • Multipurpose Internet Mail Extensions (MIME) permits transfer of nontextual information (e.g., images)

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