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

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%

Electronic Mail

Among most widely used Internet services

Two major components User interface Mail transfer software

Paradigm: transfer is separate background activity

Illustration Of Email System Components

Mailbox Names And Aliases

Email destination identified by pair( mailbox, computer )

Aliases permitted (user enters alias that is expanded)

Forwarding

Powerful idea Email arriving on a computer can

be forwarded to an ultimate destination

Illustration Of Aliases And Forwarding

TCP/IP Standards For Email

Syntax for email addresses Format of email message Protocols for email transfer and

mailbox access

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

Format Of Email Message

Message consists of Header Blank line Body of message

Headers have formkeyword : information

Standard given in RFC 2822

E-mail headerReturn-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 2.2Received: 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 PlayDate: Fri, 28 Apr 2006 14:14:39 -0400Message-ID: <003101c66aef$a9e2f830$81446f82@NETUMFK.EDU>MIME-Version: 1.0Content-Type: multipart/alternative;

boundary="----=_NextPart_000_0032_01C66ACE.22D15830"X-Mailer: Microsoft Office Outlook 11X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2869Thread-index: AcZq75BMY/2KYcRVRGurpMOPNTltNA==X-MailScanner-Information: Please contact the ISP for more informationX-MailScanner: Found to be cleanX-MailScanner-From: voisine@maine.edu

Protocol For Email Transfer

Specifies interaction between transfer components Transfer client Transfer server

Standard protocol is Simple Mail Transfer Protocol (SMTP)

SMTP

Application-level protocol Uses TCP Commands and responses

encoded in ASCII

Example Of SMTP

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

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

MIME Header Header in email message describes

encoding used Example

From: bill@acollege.eduTo: john@example.comMIME-Version: 1.0Content-Type: image/jpegContent-Transfer-Encoding: base64

...data for the image...

Seven Basic MIME Types

Example Of Mixed / Multipart Message

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)