Summary

SMTP protocol

• SMTP: Simple Mail Transfer Protocol
  • Protocol for sending email messages between mail servers
  • Uses TCP port 25 (or 587 for submission)
  • Client-server model (client initiates connection to server)
  • Commands (ASCII text) and responses (status code and phrase)
    • e.g., HELO, MAIL FROM, RCPT TO, DATA
  • Supports authentication and encryption (e.g., STARTTLS)

3 phases of transfer:

• SMTP handshaking
• SMTP transfer of messages
• SMTP connection closing

Command Example

Retrieving email protocols

• SMTP: delivery/storage of e-mail messages to receiver’s server
  • port 25, 587 (TLS)
• IMAP: messages stored on server
  • provides retrieval, deletion, folders of stored messages on server
  • port 143, 993 (TLS)
• HTTP: gmail, Hotmail, Yahoo, etc.
  • provides web-based interface on top of STMP (to send), IMAP (or POP) to retrieve e-mail messages
• POP 3: for server when user wants to have access only using one device