Simple Mail Transfer Protocol (SMTP) - PowerPoint PPT Presentation

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Simple Mail Transfer Protocol (SMTP)

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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 ... – PowerPoint PPT presentation

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Title: Simple Mail Transfer Protocol (SMTP)


1
Simple Mail Transfer Protocol(SMTP)
  • CS-328
  • Dick Steflik

2
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)

3
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

4
SMTP Commands
HELO ltspgt ltdomaingtltcrlfgt MAIL ltspgtFROMltreverse
pathgtltcrlfgt RCPT ltspgtTOltforward
pathgtltcrlfgt DATAltcrlfgt terminates with
ltcrlfgt.ltcrlfgt RSETltcflfgt SENDltspgtFROMltreverse
pathgtltcrlfgt SOMLltspgtFROMltreverse
pathgtltcrlfgt SAMLltspgtFROMltreverst
pathgtltcrlfgt VRFYltspgtltstringltcrlfgt EXPNltspgt
ltstringgtltcrlfgt HELPltspgtltstringgtltcrlfgt NOOPltcrlfgt Q
UITltcflfgt TURNltcflfgt
5
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
  • ltcrgt.ltcrgt tells server data transfer is over

6
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  • like MAIL, outdated not used any more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

7
Commands
  • HELP
  • ask server for help
  • by itself get a list of server supported commands
  • ltstringgt 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

8
Reply codes
  • 211 - System status or help ready
  • 214 - Help message
  • 220 - ltdomaingt Service ready
  • 221 - ltdomaingt Service closing transmission
    channel
  • 250 - Requested mail action OK, ready
  • 251 - User not local, will forward to ltforward
    pathgt
  • 354 - Start mail input end with ltcrlfgt.ltcrlfgt
  • 421 - ltdomaingt 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

9
Reply codes (more)
  • 550 - Requested action not taken, mailbox
    unavailable
  • 551 - User not local, please try ltforward pathgt
  • 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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