Email

1
Email

• WeeSan Lee ltweesan_at_cs.ucr.edugt
• http//www.cs.ucr.edu/weesan/cs183/

2
Roadmap

• Introduction
• Mail System Architecture
• Email Headers
• Sendmail
• Debugging
• Aliases
• Forwarding
• Procmail
• QA

3
Introduction
The Internet
MUA Eudora
MTA (port 25)
MTA (port 25)
MUA Outlook
LDA procmail
MUA mail
MUA mail
MSA (port 587)
Message store
MUA pine
MUA pine
AA Imapd, pop3
4
Introduction (cont)

• A mail system consists of
• MUA Mail User Agent
• Lets users read and compose email, eg. Mail,
  Pine, Eudora, Outlook
• MTA Mail Transport Agent
• Routes emails among machines, eg. Sendmail,
  Postfix
• Speaks SMTP (Simple Mail Transport Protocol)
• MSA Mail Submission Agent
• Accepting emails from MUA, eg. Sendmail
• LDA Local Delivery Agent
• Places emails to a local message store, eg.
  Procmail
• /var/spool/mail/username
• AA Access Agent
• Connects MUA to message store, eg. POP3, IMAP

Question What are the differences between POP3
and IMAP?
5
Mail System Architecture

• Incoming SMTP server
• For accepting incoming emails with spam filters
• Outgoing SMTP server
• For sending outgoing emails
• IMAP or POP3 server
• For retrieving emails
• Message Store
• /var/spool/mail/username
• /home/username/mail/INBOX

6
E-mail

• Header
• Attribute value
• Eg.
• From weesan_at_cs.ucr.edu
• Bcc bill.gates_at_microsoft.com
• Header starts with X- will be ignored, eg.
• X-Spam-Flag YES
• Body
• 7-bit ASCII text
• Question How are binary data sent over emails?

7
Sendmail

• Both a MTA (port 25) and MSA (port 587)
• Configuration file
• /etc/mail/sendmail.cf
• Mail queue
• /var/spool/mqueue/

8
Debugging

• mail
• cal mail -s test weesan_at_cs.ucr.edu
• sendmail -oi -t
• cat sendmail -oi t
• From weesan_at_cs.ucr.edu
• To bill.gates_at_microsoft.com
• Subject Hi Bill
• Linux is better ?
• -WeeSan
• D

9
Debugging (cont)

• telnet
• telnet mail.cs.ucr.edu 25
• 220 esmtp.cs.ucr.edu ESMTP Postfix
• mail from weesan_at_cs.ucr.edu
• 250 Ok
• rcpt to bill.gates_at_microsoft.com
• 250 Ok
• data
• 354 End data with ltCRgtltLFgt.ltCRgtltLFgt
• Subject Hi Bill
• Linux is better )
• .
• 250 Ok queued as F1C832AFBE4
• quit
• 221 Bye
• Connection closed by foreign host.

10
/etc/aliases or /etc/mail/aliases

• Allows users to be referred by multiple names
• Used by mailing list
• cat /etc/aliases grep weesan
• root weesan, weesan_at_email.com
• To rehash aliases
• newaliases

11
/.forward

• cat /.forward
• \weesan
• weesan_at_email.com

12
/.procmailrc

• For spam
• 0
• (Subject.\SPAM\X-Spam-Flag YES)
• INBOX.spam
• Another type of spam ?
• 0
• From.bill.gates_at_microsoft.com
• /dev/null

13
/.procmailrc

• SMS myself
• 0 c
• From.myboss_at_ucr.edu
• (formail -c -XFrom -XSubject echo "To
  MY_CELL") SENDMAIL -oi -t

14
/.procmailrc

• UCR Systems support emails
• 0
• Subject.(New TicketTicket Assigned)
• 0 c
• INBOX.systems
• 0
• (formail -c -XFrom -XSubject echo "To
  MY_CELL") SENDMAIL -oi -t

15
Reference

• LAH
• Ch 18 Electronic Mail
• http//www.sendmail.org/
• http//www.procmail.org/
• http//www.imap.org/