Web server administration chap08

Web Server Administration

Chapter 8
Providing E-mail Services

1


Overview







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
e-mail 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




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)







MUA (Mail User Agent)





Accepts e-mail from clients and sends email 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





Relaying






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)





POP3 (Post Office Protocol)





To send e-mail messages
To retrieve e-mail
Typically, all messages are downloaded to a
client

IMAP4 (Internet Mail Access Protocol)




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:
250 2.1.0 OK
RCPT TO:
250 2.1.5
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:
Return-Path:
This is a sample message
.
DELE 1
+OK
QUIT

15


Understanding IMAP4




Messages remain on server
Requires much more space on server
To keep track of the status of messages,
flags are used








\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









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


Messag
e
Deliver
y
Default
s

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






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





SMTP server IP address
Your e-mail address
Your e-mail password
POP3 or IMAP4 server IP address

25