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Simple Mail Transfer Protocol (SMTP). CS-328 Dick Steflik. SMTP RFCs. RFCs - 821, 1870, 1891 Related RFCs RFC 822 (Mail) RFC 1521 (MIME) RFC - 1725 (POP3) RFC - 1730 (IMAP4) Well known port : 25 (TCP) . SMTP Process. Contact server on well known port ASCII oriented command/response

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Simple mail transfer protocol smtp

Simple Mail Transfer Protocol(SMTP)

CS-328

Dick Steflik


Smtp rfcs
SMTP RFCs

  • RFCs - 821, 1870, 1891

  • Related RFCs

    • RFC 822 (Mail)

    • RFC 1521 (MIME)

    • RFC - 1725 (POP3)

    • RFC - 1730 (IMAP4)

  • Well known port : 25 (TCP)


Smtp process
SMTP Process

  • Contact server on well known port

  • ASCII oriented command/response

  • methodology

    • contact server

    • wait for greeting

    • send HELO

    • wait for response

    • send command

    • wait for response

    • repeat last two


Smtp commands
SMTP Commands

HELO <sp> <domain><crlf>

MAIL <sp>FROM:<reverse path><crlf>

RCPT <sp>TO:<forward path><crlf>

DATA<crlf> terminates with <crlf>.<crlf>

RSET<cflf>

SEND<sp>FROM:<reverse path><crlf>

SOML<sp>FROM:<reverse path><crlf>

SAML<sp>FROM:<reverst path><crlf>

VRFY<sp><string<crlf>

EXPN<sp> <string><crlf>

HELP<sp><string><crlf>

NOOP<crlf>

QUIT<cflf>

TURN<cflf>


Commands
Commands

  • HELP

    • identifies the client to the server, fully qualified domain name, only sent once per session

  • MAIL

    • initiate a message transfer, fully qualified domain of originator

  • RCPT

    • follows MAIL, identifies an addressee, typically the fully qualified name of the addressee

    • for multiple addressees use one RCPT for each addressee

  • DATA

    • send data line by line

    • <cr>.<cr> tells server data transfer is over


Commands1
Commands

  • RSET

    • tells server to abort current message and clear all of it buffers

    • same state as after HELO

  • SEND , SOML , SAML

    • like MAIL, outdated not used any more

  • VRFY

    • ask server to verify a user name

    • server replies positively of it knows user, negatively if not

  • EXPN

    • ask server to confirm mailing list alias

    • server reply is multi-line, one per user


Commands2
Commands

  • HELP

    • ask server for help

      • by itself get a list of server supported commands

      • <string> get help for that command

  • NOOP

    • ask server to respond with a positive reply

  • QUIT

    • tell server that client is ending session

    • server replies positively and closes connection

  • TURN

    • reverse roles of client and server

      • outdated, rarely used on modern internet


Reply codes
Reply codes

  • 211 - System status or help ready

  • 214 - Help message

  • 220 - <domain> Service ready

  • 221 - <domain> Service closing transmission channel

  • 250 - Requested mail action OK, ready

  • 251 - User not local, will forward to <forward path>

  • 354 - Start mail input; end with <crlf>.<crlf>

  • 421 - <domain> Service not avail, closing transmission channel

  • 450 - Requested mail action not taken, mailbox not available

  • 451 - Requested action aborted, local error

  • 452 - Requested action not taken, insufficient storage

  • 500 - Syntax error, command unrecognized

  • 501 - Syntax error in parameters

  • 502 - Command not implemented

  • 503 - Bad sequence of commands

  • 504 - Command Parameter not implemented


Reply codes more
Reply codes (more)

  • 550 - Requested action not taken, mailbox unavailable

  • 551 - User not local, please try <forward path>

  • 552 - Requested mail action not taken; exceeded storage allocation

  • 553 - Requested action not taken, mailbox name not allowed

  • 554 - Transaction failed


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