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 MAIL FROM: RCPT TO: DATA terminates with. RSET SEND FROM: SOML FROM: SAML FROM: VRFY EXPN HELP NOOP QUIT TURN

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 –. 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server to abort current message and clear all of it buffers –same state as after HELO SEND, SOML, SAML –like MAIL, outdated not used any more VRFY –ask server to verify a user name –server replies positively of it knows user, negatively if not EXPN –ask server to confirm mailing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 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that client is ending session –server replies positively and closes connection TURN –reverse roles of client and server outdated, rarely used on modern internet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 - Service ready 221 - Service closing transmission channel 250 - Requested mail action OK, ready 251 - User not local, will forward to 354 - Start mail input; end with. 421 - 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 552 - Requested mail action not taken; exceeded storage allocation 553 - Requested action not taken, mailbox name not allowed 554 - Transaction failed