23-AL-SMTP - Ele ctronic Mail and S MTP 1 Ele ctronic Mail...

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1 Electronic Mail and SMTP
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2 Electronic Mail System components: user agents mail servers simple mail transfer protocol: SMTP – TCP port 25 User Agent a.k.a. “mail reader” composing, editing, reading mail messages e.g., Eudora, Outlook, elm, Netscape Messenger outgoing, incoming messages stored on server user mailbox outgoing message queue mail user agent SMTP
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3 Electronic Mail: Issues ISSUES 1. How does UA talk to mail server to send a mail 2. How does a mail server talk to another mail server to send a mail 3. to retrieve a mail 1 and 2 – SMTP 3 – PO3, IMAP mail server user agent SMTP POP3 IMAP
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4 Electronic Mail: SMTP [RFC 2821] uses TCP to reliably transfer email message from client to server, port 25 direct transfer: sending server to receiving server three phases of transfer handshaking (greeting) transfer of messages closure command/response interaction commands: ASCII text response: status code and phrase messages must be in 7-bit ASCII
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5 Scenario: Alice sends message to Bob 1) Alice uses UA to compose message and “to” bob@someschool.edu 2) Alice’s UA sends message to her mail server; message placed in message queue 3) Client side of SMTP opens TCP connection with Bob’s mail server 4) SMTP client sends Alice’s message over the TCP connection
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23-AL-SMTP - Ele ctronic Mail and S MTP 1 Ele ctronic Mail...

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