ESMTP

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ESMTP
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ESMTP Intro

• 1982 SMTP was first formalized.
• SMTP is used by MUAs to send mail messages to
  MTAs and by MTAs to transfer mail to other MTAs.
• The many extensions to SMTP have become ESMTP.

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Using ESMTP

• Between a client that wishes to send a message
  and a server that will accept it for delivery
  (destination mailbox or another server)
• Envelope the address of sender and receiver,
  date, time
• Different from the address of message header

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ESMTP Commands

• No support structured states except mail
  transaction state (MAIL, RCPT, DATA, REST)

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Commands 1

• that may occur at any time
• HELO used to identify the client
• EHLO to identify the client and requests a list
  of ESMTP service extensions supported by server
• VRFY asks the server if it can verify that the
  username or email address given maps to a local
  user
• EXPN asks the server if it can expand the
  mailing list

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Commands 1_ Cont

• HELP
• NOOP
• TURN requests that the client and server
  exchange roles
• VERB
• ETRN processes the mail queue for the specified
  host, domain, or queue.
• QUIT

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Minimal SMTP commands

• HELO
• MAIL
• RCPT
• DATA
• RSET

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Server Response Code

• Consists of 3 digits
• First digit
• 1 not used
• 2 the command has completed successfully
• 3 The current command requires more command
• 4 temporary failure
• 5 an error has occurred.

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Server Response Code (cont

• 2nd digit category of the status
• 0 syntax error
• 2 connection status
• 5 mail system status
• 1, 3, 4 not defined yet.

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Mail Transaction Commands

• Client MAIL FROM byron_at_dogbone.net RETFULL
• Server 250 byron_at_dogbone.net Sender ok
• DSN (Delivery Status Notification)
• RETFULL OR HDRS
• Client RCPT TO blueberry_at_powerup.com
  NOTIFYSUCCESS, FAILURE, DELAY
• Server 250 blueberry_at_powerup.comRecipient ok