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user agent user agent sender’s mail server SMTP Mail Access Protocols SMTP access Protocol POP3, IMAP, or HTTP receiver’s mail server
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ITEC4621 Network Security SMTP: delivery/storage to receiver’s server Mail access protocol: retrieval from server POP: Post Office Protocol authorization (agent server) and download IMAP: Internet Mail Access Protocol more features (more complex) manipulation of stored messages on server HTTP (web-based email): Hotmail, Yahoo! Mail, etc. ITEC4621 Network Security Uses TCP to reliably transfer email message from client to server, port 25 Direct transfer: sending server to receiving server via many Mail Transfer Agents (MTAs) user agent user agent mail server mail server SMTP Protocol 1 2 6 3 4 5 ITEC4621 Network Security Mail Servers mailbox contains incoming messages for user messagequeue of outgoing (to be sent) mail messages SMTP protocol Deliver emails from user agent to user’s mail server Deliver emails between mail servers user agent user agent user agent user agent user agent user agent SMTP SMTP SMTP mail server mail server mail server Electronic Mail (cont.) ITEC4621 Network Security Three major components: user agents (UAs) mail servers simple mail transfer protocol: SMTP Mail Transfer Agents (MTAs) User Agent Known as “mail reader” composing, editing, reading mail messages e.g., Eudora, MS Outlook, Outlook Express, Netscape Messenger outgoing, incoming messages stored on server user agent user agent user agent user agent user agent user agent SMTP SMTP SMTP mail server mail server mail server outgoing message queue user mailbox Overview of Electronic Mail ITEC4621 Network Security Lecture 07 PGP and S/MIME Supakorn Kungpisdan, Ph.D.