SMTP at a glance

1
SMTP at a glance

• TechSem C0312M

2
STMP A quick glance

• SMTP Overview
• A brief history of SMTP
• SMTP technical review
• SMTP commands
• SMTP and Java
• Further readings

3
SMTP - Overview

• What is SMTP?
• Email looking back
• Simple Mail Transfer Protocol
• Operates at application layer (OSI)
• Runs over TCP/IP

4
Why SMTP?

• Email the most popular service
• The email protocol wars
• X400, MOTIS

5
A brief history of SMTP

• Mail Transfer Protocol (MTP)
• RFC 780 (05/1980)
• FTP-based
• Simple Mail Transfer Protocol (SMTP)
• RFC 788 (11/1980)
• Simple, independent

6
A brief history of SMTP contd.

• Simple Mail Transfer Protocol (SMTP)
• RFC 821 822 (8/1982)
• Extended SMTP (ESMTP)
• SMTP service extensions
• RFC 1425 (3/1993)

7
SMTP today

• Latest SMTP standards
• RFC 2821 2822 (04/2001)
• Includes ESMTP
• ESMTP for transmission of Large and Binary MIME
• RFC 3030 (12/2000)

8
SMTP A technical view

• Basic informations
• Standard port 25
• Clear-text protocol
• Mail relaying
• Stored in POP or IMAP server
• Message format (RFC 2822)
• MIME (Multipurpose Internet Mail Extensions)
• RFC 2045 ? 2049

9
SMTP - Commands

• What is SMTP commands?
• Text command CRLF
• Parameters
• Command list
• HELO, EHLO, MAIL, RCPT, DATA
• RSET, NOOP, QUIT, VRFY
• HELP, EXPN

10
SMTP command sequence

• Basic command sequence
• EHLO / HELO
• MAIL
• RCPT
• DATA
• QUIT

11
SMTP commands HELO, MAIL

• HELO / EHLO
• Syntax EHLO ltDomaingt
• Usage indentify mail clients
• MAIL
• Syntax MAIL FROM ltsender addressgt
• Usage Start a new mail transaction

12
SMTP commands RCPT, DATA

• RCPT (recipient)
• Syntax RCPT TO ltrecipient addressgt
• Usage identify an individual recipient
• DATA
• Syntax DATA (ends with CRLF . CRLF)
• Usage specify the actual message

13
SMTP commands RSET, QUIT

• RSET (reset)
• Syntax RSET
• Usage Abort the current transaction
• QUIT
• Syntax QUIT
• Usage Terminate the connection

14
SMTP commands VRFY, NOOP

• VRFY (verify)
• Syntax VRFY ltusernamegt
• Usage confirm a user or mailbox
• NOOP
• Syntax NOOP
• Usage request an OK reply from the server

15
SMTP commands EXPN, HELP

• EXPN
• Syntax EXPN ltmailing listgt
• Usage confirm a mailing list
• HELO
• Syntax HELP ltcommandgt
• Usage HELP display command list
• Usage display command syntax and usage

16
SMTP reply code

• 211 system status
• 220 system ready (welcome)
• 250 OK
• 354 DATA input
• 50x syntax error

17
SMTP telnet demo
C\gttelnet localhost 25 220 localhost ESMTP at
your service helo localhost 250 localhost Hello
localhost 127.0.0.1, pleased to meet you. mail
fromadmin_at_localhost 250 2.1.0 ltadmin_at_localhostgt..
. Sender ok rcpt to test_at_localhost 250 2.1.5
lttest_at_localhostgt... Recipient ok data 354 Enter
mail, end with "." on a line by
itself Tihadsjkfnwefsiondsjfnkjsd This is a test
mail sekhfsdjfsssdjfushfsdhkfsd . 250 2.6.0 80
bytes received in 000021 Message accepted for
delivery quit 221 2.0.0 localhost closing
connection
18
SMTP and Java

• Implementations with Java Networking
• Pure socket
• Socket port 25
• JavaMail API
• SMTP and C0312M

19
SMTP Summary

• General info on SMTP
• Technical info on SMTP\
• SMTP commands
• SMTP and Java

20
Further readings

• RFCs
• SMTP RFC 2821, 2822
• MIME RFC 2045, 2046, 2047, 2048, 2049
• SMTP tutorials