1. Lesson 26 - (1 of 41) E-mail, SMTP, and MIME types

2. Lesson 26 - (2 of 41) Outline: E-mail, SMTP, and MIME types Mail Systems: –Terminology –Delayed Delivery Names and Aliases: Controlling E-Mail Messages: Internetworking and Mail: Mail Gateways: Mail Addresses: Simple Mail Transfer Protocol (SMTP): Post Office Protocol (POP) E-Mail Application Program Interfaces: –MAPI –AOCE MIME Extensions MIME Types and Subtypes S/MIME Content Type MIME Multipart Messages

3. Lesson 26 - (3 of 41) Mail Systems: Interactive Client / Server Message Exchange: –Messages can be generated and delivered using an electronic mail client. –Those messages are then passed point-to-point, from e-mail server to e-mail server, until delivered or rejected.

4. Lesson 26 - (4 of 41) Mail Systems: Mail systems differ from normal network delivery since the absolute destination can be down or the mail recipient may not be on-line (delayed delivery). Similar to conventional mailing schemes, e-mail allows a server to place successfully delivered mail in the recipients mailbox.

5. Lesson 26 - (5 of 41) Mail Systems: Terminology Terminology: –E-mail (Electronic Mail) - most computers support e-mail of different types and over different operating platforms (delivery times range from seconds...hours or days.) –Snail Mail (Conventional Mail) - post office is used and manually delivered (takes several days).

6. Lesson 26 - (6 of 41) Mail Systems: Delayed Delivery Spooling or Mail Queues store mail messages the user sends in a private area, which include the following information: –ID of sender –ID recipient –Destination machine address –Time of deposit

7. Lesson 26 - (7 of 41) Mail Systems: Delayed Delivery After spooling messages, the system then initiates the transfer to the remote machine as a background activity. Spooled messages can be sent at various times in block amounts (transfer process sweeps through the spool area periodically).

8. Lesson 26 - (8 of 41)...... outgoing mail spool area mailboxes for incoming mail client (background transfer) server (to accept mail) user send mail user reads mail TCP connection for outgoing mail user inter- face Components of an E-Mail System:

9. Lesson 26 - (9 of 41) Names and Aliases: Recipients specified by pair of identifiers: –Mail destination machine name. –Mailbox address on that machine. Mail machine names and mailboxes can be assigned independently of other names assigned to a machine (position of employment or responsibility).

10. Lesson 26 - (10 of 41) Names and Aliases: The domain name system (DNS) supports a database and query type for mail destinations. This makes it possible to de-couple mail destination names from usual domain names for machines. Some e-mail packages require explicit DNS commands be used when sending e-mail (VAX/VMS requires MX%”name”)

11. Lesson 26 - (11 of 41) Controlling E-Mail Messages: Methods of sending e-mail: –One-to-one. –One to a group of e-mail addresses (all specified each time). –Mail Aliases –Mail Exploder (listservers) –Majordomo (automated response e-mail)

12. Lesson 26 - (12 of 41) Controlling E-Mail Messages: Mail Alias Expansion (mail forwarder): –Allows the local site to map identifiers used in mail addresses to a set of new mail addresses (electronic mailing lists, mail forwarding). –Files can be setup in UNIX accounts to allow e- mail messages to automatically be forwarded to another specified e-mail account.

13. Lesson 26 - (13 of 41) Controlling E-Mail Messages: Mail Exploder: –Accepts one incoming message and sends it to a large set of recipients. –Acts as an alias for a group destinations where a copy is sent to each member (listservers).

14. Lesson 26 - (14 of 41)...... outgoing mail spool area mailboxes for incoming mail alias expansion and forwarding server (to accept mail) user sends mail user reads mail client (background transfer) alias database user inter- face

15. Lesson 26 - (15 of 41) Internetworking and Mail: Commercial e-mail systems differ from TCP/IP in two crucial ways: –TCP/IP on the Internet creates a universal delivery service. –E-mail systems built on TCP/IP are more reliable (TCP provides end-to-end connectivity).

16. Lesson 26 - (16 of 41) Internetworking and Mail: Mail systems that use end-to-end delivery can guarantee that each mail message remains in the sender’s machine until it has been successfully copied to the recipient’s machine.

17. Lesson 26 - (17 of 41) Mail Gateways: Mail Gateways (mail bridges): –Are not end-to-end, but send mail across intermediate machines that forward the mail messages. –Advantage - provides interoperability between various e-mail systems and networks. –Disadvantage - introduces unreliability.

18. Lesson 26 - (18 of 41) Mail Gateways: TCP/IP mail standard has two main parts: –Specifies the format for mail messages and their headers. –Specifies the details of electronic mail exchange.

19. Lesson 26 - (19 of 41) Mail Addresses: Connected Internet addresses are simple: (localpart@domain-name) –Localpart - usually a user’s ID or account name. –Domain-name - officially registered with the IAB, this name is usually structured to reflect: Machine name. Site name. Top-level domain.

20. Lesson 26 - (20 of 41) Mail Addresses: Outside connected Internet addresses are complex since mail address mapping functions are local to each machine. They are not always in domain-name format. –dzt!mttec@mt.att.com –comer%purdue.edu@relay.cs.net

21. Lesson 26 - (21 of 41) Simple Mail Transfer Protocol (SMTP): –This protocol focuses specifically on how the underlying mail delivery system passes messages from machine to machine. –It is an official TCP/IP standard application protocol.

22. Lesson 26 - (22 of 41) Simple Mail Transfer Protocol (SMTP): It provides readable text transcripts of client- server interactions in the mail header and integer values for commands: –MAIL FROM –RCPT TO –HELO –250 OK –QUIT

23. Lesson 26 - (23 of 41) Example SMTP Interaction: S:hertz.njit.eduSimple Mail Transfer Service Ready. C:HELOpegasus.rutgers.edu S:250hertz.njit.edu C:MAIL FROM: S:250OK C:RCPT TO: S:250OK

24. Lesson 26 - (24 of 41) Example SMTP Interaction: (Continued) C:DATA S:354 Start mail input; end with. C:…sends body of mail message… C:…continues for as many lines as message contains C:. S:250OK C:QUIT S:221 hertz.njit.eduService closing transmission.

25. Lesson 26 - (25 of 41) Post Office Protocol (POP): Post Office Protocol - Version 3 (POP3): –Is intended to permit a workstation to dynamically access a maildrop (mail server) on a server host in a useful fashion. –Usually, this means that the POP3 is used to allow a workstation to retrieve mail that the server is holding for it. –Access to a POP3 server requires a username and password.

26. Lesson 26 - (26 of 41) E-Mail Application Program Interfaces: MAPI Messaging Application Program Interface (MAPI): –Is a set of messaging functions that helps you create mail-enabled applications as well as other message-based applications. –With MAPI functions, you can easily add messaging to any Windows application and may or not include a user interface (a dialog box). –It is supported by many vendors (Microsoft).

27. Lesson 26 - (27 of 41) E-Mail Application Program Interfaces: AOCE What is AOCE? –AOCE stands for Apple Open Collaboration Environment. –It is a set of technologies that provide for system-level collaboration and messaging services. –The first incarnation of AOCE was in the form of PowerShare and PowerTalk, the AOCE server and client, respectively. –It is a proposed standard interface to e-mail.

28. Lesson 26 - (28 of 41) MIME Extensions: Multipurpose Internet Mail Extensions (MIME): –Defined by IETF to allow transmission of non- ASCII data via e-mail. –It allows arbitrary data to be encoded in ASCII for normal transmission. –All media types that are sent/received over the World Wide Web are encoded using different MIME types.

29. Lesson 26 - (29 of 41) MIME Extensions: 822 Mail Header Messages sent using MIME encoding include information that describes the type of data and the encoding that was used (resides in 822 mail header). 822 Mail Header: –Version of MIME used. –Type of data sent. –Encoding method used.

30. Lesson 26 - (30 of 41) Example 822 Mail Message Header: From:dzt@mttec.mt.att.com To:jverga@pegasus.rutgers.edu MIME-Version:1.0 Content-Type:image/gif Content-Transfer-Encoding:base64 …data for the image...

31. Lesson 26 - (31 of 41) MIME Types and Subtypes: All different media encoding done in MIME is classified as a combination of types and subtypes. Each MIME Content-Type must contain two identifiers: –Content Type –Content Subtype

32. Lesson 26 - (32 of 41) MIME Types and Subtypes: There are seven official (standardized) content- types that can appear in a MIME Content-Type declaration: –Text - Textual documents. –Image - A computer generated image. –Audio - A sound file. –Video - A motion video recording.

33. Lesson 26 - (33 of 41) MIME Types and Subtypes: –Application - Raw data for a program. –Multipart - Multiple messages, each having a separate content type and encoding. –Message - An entire e-mail message or an external reference to a message (FTP server and filename).

34. Lesson 26 - (34 of 41) MIME Types and Subtypes: An eight type has been proposed and will most likely be approved to supply a secure method for transferring encoded data: –Secure - Data is sent encrypted and in a secure fashion. The push for an official secure MIME content- type has come about due to the increased interest in doing business over the WWW.

35. Lesson 26 - (35 of 41) S/MIME Content Type: What is S/MIME? –A specification for secure electronic mail. –S/MIME stands for Secure/Multipurpose Internet Mail Extensions and was designed to add security to e-mail messages in MIME format. The security services offered are authentication (using digital signatures) and privacy (using encryption).

36. Lesson 26 - (36 of 41) S/MIME Content Type: Why S/MIME? –In the growing demand for e-mail security, S/MIME melds proven cryptographic constructs with standard e-mail practices. Is S/MIME a standard? –No. Although the S/MIME spec will be submitted to the IETF for consideration as an official Internet RFC (standard) when interoperability tests are complete.

37. Lesson 26 - (37 of 41) MIME Types and Subtypes: Examples of Content Type/ Subtype: –image/jpeg –text/html –video/mpeg –audio/x-wav –application/octet-stream

38. Lesson 26 - (38 of 41) MIME Multipart Messages: Multipart content type has four subtypes, each of which adds significant flexibility to MIME encoding: –Mixed - allows a single message to contain multiple independent sub-messages, each of which is separately encoded (HTML documents with images).

39. Lesson 26 - (39 of 41) MIME Multipart Messages: –Alternative - a single message can include multiple representations of the same data type (ASCII and Rich Text Format). –Parallel - a single message that includes subparts which should be viewed together (video with audio). –Digest - a single message that can contain a set of other messages (e-mail messages from a discussion).

40. Lesson 26 - (40 of 41) Questions E-mail, SMTP, and MIME types Why do you think MIME-encoded messages used as the foundation of WWW technology? How does one setup a mail-reflector in there account to forward e-mail? A listserv is a special type of e-mail broadcasting. Explain. What are Mail APIs used for? Give an example. What specific MIME type(s) would be used to send an HTML page with in-line video/audio support?

41. Lesson 26 - (41 of 41) Reference Materials E-mail, SMTP, and MIME types RFC 1651, 1652, 1653: SMTP Services (http://www.cis.ohio-state.edu/htbin/rfc/rfc1651.html) E-Mail API Web Resources: (http://andrew2.andrew.cmu.edu/cyrus/email/standards-apis.html) RFC 1081, 1082: Post Office Protocol - Version 3 (http://www.cis.ohio-state.edu/htbin/rfc/rfc1081.html) Writing your own SMTP gateway: (http://www.vb-online.com/sep95/smtp.html) RFC 1521, 1522: MIME Extensions and Headers (http://www.cis.ohio-state.edu/htbin/rfc/rfc1521.html)