Web Server Administration
Chapter 8
Providing E-mail Services
1
Overview

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

Understand the e-mail environment
Understand e-mail protocols
Install and administer Microsoft
Exchange 2000
Install and administer sendmail for
Linux
2
Overview



Install and configure IMAP4 and POP3
servers for Linux
Configure e-mail clients
Understand Web-based e-mail clients
3
Understanding the E-mail
Environment



E-mail evolved from a variety of proprietary
systems
In the 1980s and 1990s, people often had email addresses on a number of systems
Even as late as 1997, Exchange 5.5 was not
designed to take advantage of Internet e-mail

An add-on gave Exchange the ability to send and
receive e-mail over the Internet
4
Exchange 2000 Goes Beyond
E-mail Basics


Instant messaging
Unified messaging platform



Chat service
URL addressing

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Single inbox for e-mail, voicemail, fax
Use a single URL to access stored data
Audio and video conferencing
5
Role of DNS in E-mail Systems

A domain name, such as technowidgets.com,
needs to be associated with two IP addresses



One IP address can be for a Web site
Another IP address is for e-mail
To associate a domain name, or any other host
name, with the IP address of an e-mail server,
you need an MX record
technowidgets.com. IN

MX 10 mail.technowidgets.com.
The 10 refers to the priority of the e-mail server
if there are multiple e-mail servers
6
E-mail System Terminology

MTA (Mail Transfer Agent)
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MUA (Mail User Agent)

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
Accepts e-mail from clients and sends e-mail to
another MTA for storage
Exchange 2000, sendmail
E-mail client
Outlook, KMail
MDA (Mail Delivery Agent)


Delivers e-mail from server to MUA
Exchange 2000, imap-2001
7
E-mail System Terminology

Masquerading

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Relaying

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
Replace actual host name with domain name
The process of sending e-mail to an intermediate
e-mail server before the message is transmitted to
its final destination
This should not be allowed from the Internet
because spammers could use it to send e-mail
Spammer

Someone who sends unsolicited e-mail, typically to
try to sell something
8
E-mail Protocols

SMTP (Simple Mail Transfer Protocol)
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
POP3 (Post Office Protocol)

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To send e-mail messages
To retrieve e-mail
Typically, all messages are downloaded to a client
IMAP4 (Internet Mail Access Protocol)

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To retrieve e-mail
E-mail stays on the server
You can create folders on server to store e-mail
9
Understanding SMTP

The commands are processed by the
SMTP server
Command
Purpose
HELO
Identifies the domain sending the message
DATA
Indicates the body of the message
VRFY
Verifies the e-mail user
QUIT
Ends the SMTP session
10
Understanding SMTP

The SMTP headers add descriptive information
Header
Description
MAIL FROM:
Identifies who is sending the message (required)
RCPT TO:
Identifies the recipient of the message (required)
RECEIVED:
Identifies the e-mail server that processed the message
DATE:
Indicates the date of the e-mail
FROM:
Shows the e-mail address as it is typically displayed in an e-mail client
SUBJECT:
Shows the subject of the e-mail message
TO:
Shows the recipient as it is typically displayed in an e-mail client
CC:
Sends copies of the message to a list of e-mail addresses
BCC:
Sends copies of the message to a list of e-mail addresses but does not
display the e-mail addresses
11
Understanding SMTP


Sample session
Commands and headers in bold
HELO WKS1
250 web1.technowidgets.com Hello [127.0.0.1]
MAIL FROM: XYZ@yahoo.com
250 2.1.0 xyz@yahoo.com....Sender OK
RCPT TO: cbranco@technowidgets.com
250 2.1.5 cbranco@technowidgets.com
DATA
354 Start mail input; end with <CRLF>.<CRLF>
This is a simple message
.
QUIT
12
Understanding POP3



More simplistic than IMAP4
First step is to log on with user name
and password
List, read, download, delete e-mail
13
Common POP3 commands
Command
Description
USER username Connects to POP3 server based on user name
PASS password Enters the password for the user, as in PASS: Ax6yy
LIST
Displays the message number followed by the number of
characters in the message
UIDL
Displays the unique ID for each message
RETR n
Replaces the n with a message number to retrieve that message
TOP n lines
Instead of retrieving the whole message, retrieves the number of
lines designated by the lines parameter for message number n
DELE n
Deletes message number n from the server
QUIT
Ends the session
14
Sample POP3 SessionMajor Components
USER cbranco
+OK
PASS pass
+OK User successfully logged on.
LIST
+OK 1 404
1 404
.
RETR 1
+OK
Received: from WKS1 (127.0.0.1) by web1.technowidgets.com
From: xyz@yahoo.com
Return-Path: xyz@yahoo.com
This is a sample message
.
DELE 1
+OK
QUIT
15
Understanding IMAP4

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Messages remain on server
Requires much more space on server
To keep track of the status of messages, flags
are used
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\Recent
\Seen
\Answered
\Flagged
\Deleted
\Draft
16
Common IMAP4 commands
Command
Description
LOGIN username
password
Log on to the server with your user name and password,
which are unencrypted.
SELECT mailbox
Select a mailbox before you perform mail tasks. The
default mailbox is called inbox. The response gives a
summary of mailbox information.
FETCH message(s)
item(s)
Retrieve messages. The message(s) parameter gives the
message number. The item(s) parameter determines what
part of the message is fetched—that is, individual header
items or the body of the text.
STORE message(s)
flags
Change the flags associated with a message. Typically,
this command is used to mark messages to be deleted,
undeleted, or identified as unread.
LOGOUT
End the IMAP4 session.
17
Installing Microsoft Exchange
2000


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SMTP is part of IIS, not Exchange, and needs
to be installed
NNTP (Network News Transport Protocol)
needs to be installed before Exchange and is
also part of IIS
Active Directory is required for Exchange
Once the above are installed, the Exchange
wizard guides you through a simple
installation
To use Exchange 2000 on Windows Server
2003, Exchange 2000 Service Pack 3 is
required
18
Administering Exchange 2000

Message
Delivery
Defaults
19
Administering Exchange Users


When you add a
user, you have
the option to
create a mailbox
By default, the email name is the
same as the user
name but you
can change it
20
Exchange 2000 Delivery
Restrictions


You can restrict the
size of messages
being sent and
received
The e-mail names of
senders can be
restricted too
21
Installing and Configuring
Sendmail for Linux


Installed from an rpm file
Configure sendmail through a macro
processor called m4

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
m4 /etc/mail/sendmail.mc >/etc/mail/sendmail.cf
There are many advanced features of
sendmail that make configuring it
substantially difficult
There are other e-mail servers, such as
qmail, that are easier
22
Minimal sendmail.mc File
divert(-1)
include(`/usr/share/sendmail-cf/m4/cf.m4')
OSTYPE(`linux')
define(`PROCMAIL_MAILER_PATH',`/usr/bin/procmail')dnl
FEATURE(local_procmail,`',`procmail -t -Y -a $h -d $u')dnl
MAILER(smtp)dnl
MAILER(procmail)dnl
Cwtechnowidgets.com
Notice that the strings are enclosed with a backtick and an
apostrophe as in `linux'
23
Installing and Configuring
IMAP4 and POP3 for Linux


Both IMAP4 and POP3 are included in the
imap-2001 package
Once installed, you have to enable the
daemons by either editing their configuration
files such as /etc/xinetd.d/imap or using
chkconfig


chkconfig imap on
Then you restart xinetd to recognize the
changes

service xinetd restart
24
Configuring E-mail ClientsTypical Information Required

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
SMTP server IP address
Your e-mail address
Your e-mail password
POP3 or IMAP4 server IP address
25
Web-based E-mail Clients



Web-based e-mail clients allow you to
use your browser
Exchange 2000 can be configured for
Web-based e-mail using Outlook Web
Access
Public sites, such as Microsoft's Hotmail
and Yahoo! Mail, have been very
popular
26
Web-based E-mail ClientsAdvantages

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Because a browser is used, no client configuration is
needed
The lack of configuration can significantly reduce
support costs
No specialized client software is needed
Users are not required to retrieve e-mail from specific
computers that have been configured for them
POP3 or IMAP4 protocols are not required, which
reduces server-side support
Because Web-based e-mail is not constrained by POP3
or IMAP4 protocols, a richer environment can be
developed that extends beyond basic e-mail
27
Summary




E-mail has evolved over the years
Microsoft Exchange 2000 and sendmail
are the two of the most popular e-mail
server products
DNS plays a central role in messaging
Three major protocols are involved in email

SMTP, POP3, and IMAP4
28