1 web server administration chapter 8 providing e-mail services
TRANSCRIPT
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Web Server Administration
Chapter 8Providing E-mail Services
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Overview
Understand the e-mail environment
Understand e-mail protocols Install and administer Microsoft
Exchange 2000 Install and administer sendmail for
Linux
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Overview
Install and configure IMAP4 and POP3 servers for Linux
Configure e-mail clients Understand Web-based e-mail
clients
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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
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Exchange 2000 Goes Beyond E-mail Basics
Instant messaging Unified messaging platform
Single inbox for e-mail, voicemail, fax Chat service URL addressing
Use a single URL to access stored data Audio and video conferencing
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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
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E-mail System Terminology MTA (Mail Transfer Agent)
Accepts e-mail from clients and sends e-mail to another MTA for storage
Exchange 2000, sendmail MUA (Mail User Agent)
E-mail client Outlook, KMail
MDA (Mail Delivery Agent) Delivers e-mail from server to MUA Exchange 2000, imap-2001
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E-mail System Terminology Masquerading
Replace actual host name with domain name Relaying
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
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E-mail Protocols SMTP (Simple Mail Transfer Protocol)
To send e-mail messages POP3 (Post Office Protocol)
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
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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
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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
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Understanding SMTP Sample session Commands and headers in boldHELO WKS1250 web1.technowidgets.com Hello [127.0.0.1]MAIL FROM: [email protected] 2.1.0 [email protected] OKRCPT TO: [email protected] 2.1.5 [email protected] Start mail input; end with <CRLF>.<CRLF>This is a simple message.QUIT
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Understanding POP3
More simplistic than IMAP4 First step is to log on with user
name and password List, read, download, delete e-mail
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Common POP3 commandsCommand 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
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Sample POP3 Session-Major ComponentsUSER cbranco+OKPASS pass+OK User successfully logged on.LIST+OK 1 4041 404.RETR 1+OKReceived: from WKS1 (127.0.0.1) by web1.technowidgets.comFrom: [email protected]: [email protected] is a sample message.DELE 1+OKQUIT
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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
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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.
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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
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Administering Exchange 2000 Messag
e Delivery Defaults
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Administering Exchange Users
When you add a user, you have the option to create a mailbox
By default, the e-mail name is the same as the user name but you can change it
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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
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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
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Minimal sendmail.mc Filedivert(-1)include(`/usr/share/sendmail-cf/m4/cf.m4')OSTYPE(`linux')define(`PROCMAIL_MAILER_PATH',`/usr/bin/procmail')dnlFEATURE(local_procmail,`',`procmail -t -Y -a $h -d $u')dnlMAILER(smtp)dnlMAILER(procmail)dnlCwtechnowidgets.com
Notice that the strings are enclosed with a backtick and an apostrophe as in `linux'
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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
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Configuring E-mail Clients-Typical Information Required
SMTP server IP address Your e-mail address Your e-mail password POP3 or IMAP4 server IP address
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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
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Web-based E-mail Clients-Advantages
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
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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 e-mail SMTP, POP3, and IMAP4