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concepts & protocols

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Presentation on theme: "concepts & protocols"— Presentation transcript:

1 E-mail System OPS335 R. Chan

2 Email: concepts & protocols
Mail Systems: User agents, submission agents, Transport agents, Local Delivery agents, Message stores, Access agents Protocols: SMTP (ESMTP) POP3 (POP3S) IMAP (IMAPS) more ...

3 Email system componets
UA: user agent DA: delivery agent MSA: submission Agent AA: access agent

4 UA: User Agent A.k.a Mail User Agent or email client: Read mail
Compose mail Supports: Plain text MIME – multipurpose Internet Mail Extensions e.g. /bin/mail (mailx)

5 Submission Agent Sits between UA and MTA Uses port 587 Speaks SMTP

6 Trsansport Agents Speak SMTP (now also ESMTP) See RFC 821 ... RFC 5321
Take incoming Chek recipents' addresses Rewrite recipent/sender addresses if needed Forward message to next MTA/local DA e.g. Sendmail, Postfix, MS Exchange

7 Local Delivery Agent Accepts mail from MTA
Delivers to recipients' mailboxes Notes: mail recipient could be A person A mailing list A program

8 Message store Mbox (simple – a single file)
Maildir (supports mail folders) Location and access premission /usr/spool/mail Read/write by owner

9 Access Agent Use to access message in the message store
Use POP3 or IMAP to communicate with the message store server Secure version: POP3S and IMAPS Difference between POP3 and IMAP e.g. outlook, thunderbird POP3/IMAP servers: Courier, Cyrus IMAP, Dovecot, Zimbra

10 Componets of a Mail Message
The Envelope The Headers The body of the message Examples

11 SMTP Simple Mail Transport Protocol
A clear text command/response protocol Key commands HELO, EHLO MAIL FROM: RCPT TO: DATA QUIT

12 A Smaple SMTP Session See the Demonstration

13 MTA Configuration Postfix
/etc/postfix/main.cf (see lab for basic settings) Commands: postfix postcat postconf postsuper

14 and DNS Domain name MX record Mail routing relay

15 MTA Debugging Postfix Mail Log entries - /var/log/maillog
Syslog - /var/log/messages Postfix directory /var/spool/postfix telnet [MTA IP] 25

16 Questions & Answers ??? ? ? ? ? ? ? ?


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