1. CITA 310 Section 6 Providing E-mail Services (Textbook Chapter 8)

2. Role of DNS in E-mail Systems A domain name, such as technowidgets.com, needs to be associated with at least two IP addresses One IP address can be for a Web site Another IP address is for e-mail To associate a domain name, or any other host name, with the IP address of an e-mail server, you need an MX record technowidgets.com. IN MX 10 mail.technowidgets.com. The 10 refers to the priority of the e-mail server if there are multiple e-mail servers

3. E-mail System Terminology MUA (Mail User Agent) E-mail client MTA (Mail Transfer Agent) Accepts e-mail from clients and sends e- mail to another MTA for storage MDA (Mail Delivery Agent) Delivers e-mail from server to MUA

4. E-mail Protocols SMTP (Simple Mail Transfer Protocol) To send e-mail messages POP3 (Post Office Protocol) To retrieve e-mail Typically, all messages are downloaded to a client IMAP4 (Internet Mail Access Protocol) To retrieve e-mail E-mail stays on the server You can create folders on server to store e-mail

5. Understanding SMTP The commands are processed by the SMTP server CommandPurpose HELO Identifies the domain sending the message DATA Indicates the body of the message VRFY Verifies the e-mail user QUIT Ends the SMTP session

6. Understanding SMTP The SMTP headers add descriptive information HeaderDescription MAIL FROM: Identifies who is sending the message (required) RCPT TO: Identifies the recipient of the message (required) RECEIVED: Identifies the e-mail server that processed the message DATE: Indicates the date of the e-mail FROM: Shows the e-mail address as it is typically displayed in an e-mail client SUBJECT: Shows the subject of the e-mail message TO: Shows the recipient as it is typically displayed in an e-mail client CC: Sends copies of the message to a list of e-mail addresses BCC: Sends copies of the message to a list of e-mail addresses but does not display the e-mail addresses

7. Understanding SMTP Sample session Commands and headers in bold HELO WKS1 250 web1.technowidgets.com Hello [127.0.0.1] MAIL FROM: XYZ@yahoo.com 250 2.1.0 xyz@yahoo.com....Sender OK RCPT TO: cbranco@technowidgets.com 250 2.1.5 cbranco@technowidgets.com DATA 354 Start mail input; end with. This is a simple message. QUIT

8. Understanding POP3 More simplistic than IMAP4 First step is to log on with user name and password List, read, download, delete e-mail

9. Common POP3 commands CommandDescription USER username Connects to POP3 server based on user name PASS password Enters the password for the user, as in PASS: Ax6yy LIST Displays the message number followed by the number of characters in the message UIDL Displays the unique ID for each message RETR n Replaces the n with a message number to retrieve that message TOP n lines Instead of retrieving the whole message, retrieves the number of lines designated by the lines parameter for message number n DELE n Deletes message number n from the server QUIT Ends the session

10. Sample POP3 Session- Major Components USER cbranco +OK PASS pass +OK User successfully logged on. LIST +OK 1 404 1 404. RETR 1 +OK Received: from WKS1 (127.0.0.1) by web1.technowidgets.com From: xyz@yahoo.com Return-Path: xyz@yahoo.com This is a sample message. DELE 1 +OK QUIT

11. Understanding IMAP4 Messages remain on server Requires much more space on server To keep track of the status of messages, flags are used \Recent \Seen \Answered \Flagged \Deleted \Draft

12. Common IMAP4 commands CommandDescription LOGIN username password Log on to the server with your user name and password, which are unencrypted. SELECT mailbox Select a mailbox before you perform mail tasks. The default mailbox is called inbox. The response gives a summary of mailbox information. FETCH message(s) item(s) Retrieve messages. The message(s) parameter gives the message number. The item(s) parameter determines what part of the message is fetched—that is, individual header items or the body of the text. STORE message(s) flags Change the flags associated with a message. Typically, this command is used to mark messages to be deleted, undeleted, or identified as unread. LOGOUT End the IMAP4 session.

13. Web-based E-mail Web-based e-mail allows you to use your browser Public sites, such as Gmail, Microsoft's Hotmail, and Yahoo! Mail, have been very popular

14. Web-based E-mail - Advantages Because a browser is used, no client configuration is needed The lack of configuration can significantly reduce support costs No specialized client software is needed

15. Web-based E-mail - Advantages Users are not required to retrieve e-mail from specific computers that have been configured for them POP3 or IMAP4 protocols are not required, which reduces server-side support Because Web-based e-mail is not constrained by POP3 or IMAP4 protocols, a richer environment can be developed that extends beyond basic e-mail