Practical Exercises To be completed by 4/20/2005

Postfix installation, configuration and testing

Your desktop machine, say unisys18, is going to be an e-mail client; your node host, say node18, should be configured as a Postfix e-mail server. You need to change the host names in the configurations below for those of your machines.

On the node, install Postfix

apt-get install postfix

During the installation, a configurator started:

choose "Internet site"
aliases for root "NONE"

Check /etc/postfix/main.cf and modify it as follows:

smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

myhostname = node18.rutgers.edu
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
mydestination = node18, node18.rutgers.edu, localhost.rutgers.edu, localhost
relayhost =
mynetworks = 127.0.0.0/8
mailbox_command =
mailbox_size_limit = 0
recipient_delimiter = +

Restart the server:

/etc/init.d/postfix reload

Test the server by telneting to it from the desktop, say unisys18:

telnet node18 25

Trying 192.168.5.38...
Connected to node18.rutgers.edu.
Escape character is '^]'.
220 node18.rutgers.edu ESMTP Postfix (Debian/GNU)

EHLO node18

250-node18.rutgers.edu
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250 8BITMIME

mail from: root@unisys18
250 Ok
rcpt to: root@node18.rutgers.edu
250 Ok

data
354 End data with .

Subject: test mail
Hi root.
.


press ENTER

250 Ok: queued as 1D0B8140F3

quit

Check for e-mail in file /var/mail/root on node18

Setup aliases to re-direct e-mail for root to youself on the server. Modify /etc/aliases

root:          jerry 
postmaster:    root

Run command

newaliases

Try to e-mail again something to root@node18
Install UW-IMAP server on node18:

apt-get install uw-imapd

Choose "Yes" for Allow insecure authentication using plaintext passwords.
Choose "Yes" for Continue installing libc-client without Maildir support Select "imap2 and "imaps".
Check if there are entries in /etc/inetd.conf for IMAP and IMAPS:

#:MAIL: Mail, news and uucp services.
imap2   stream  tcp     nowait  root    /usr/sbin/tcpd /usr/sbin/imapd
imaps   stream  tcp     nowait  root    /usr/sbin/tcpd /usr/sbin/imapd

To verify that the IMAP and IMAPS ports are open (tcp/143 and tcp/993), run

netstat -nalp | grep inetd

On your desktop, configure an e-mail program. It can be either Mozilla or pine. You can download the pine deb package from here
Install it

dpkg -i pine_4.61-1_i386.deb

In configuration file /etc/pine.conf, specify the name of the domain, outgoing SMTP server, and the Inbox IMAP server, for example

user-domain=node18.rutgers.edu

smtp-server=node18.rutgers.edu

inbox-path="{node18.rutgers.edu:143/novalidate-cert}inbox"

Install ntpdate on both the desktop and the node in order to synchronize the clocks. Otherwise, e-mail time stamps would be inconsistent.

apt-get install ntpdate
ntpdate -su 128.6.224.114

Run pine or Mozilla to send and receive emails at node18.rutgers.edu.

Sending e-mail to remote hosts.
Modify /etc/hosts on node18 and include a new entry for capone.rutgers.edu:

192.168.5.240           capone.rutgers.edu capone

Modify mynetworks in /etc/postfix/main.cf and also add disable_dns_lookups as follows:

mynetworks = 127.0.0.0/8  192.168.5.0/24
disable_dns_lookups = yes

Reload postfix:

/etc/init.d/postfix reload

Send an e-mail to mailtest18@capone.rutgers.edu. Note, if you are using unisys01/node01, send e-mail to mailtest01@capone.rutgers.edu, accordingly.
Retrieve the e-mail from capone by telneting to POP3 and authenticating as user mailtest18 with password 'Password18'. Note, for mailtest01, the password is 'Password01', for mailtest02, the password is 'Password02', etc:

telnet capone 110
Trying 192.168.5.240...
Connected to 192.168.5.240.
Escape character is '^]'.
+OK
USER mailtest18
+OK
PASS Password18 
+OK
RETR 1
+OK
......

DELE 1  
+OK
QUIT

Send e-mail to the other students in the class. You can use either their user name or aliased root on nodes as the recepient e-mail address, such as root@node01.rutgers.edu, root@node02.rutgers.edu, etc. Check if they can receive your e-mails.

Try to email yourself at eden or any other remote host outside of our private subnet.
The email should bounce back to you with an error like below

 5.1.8 ... Domain of sender address
 jack@node18.rutgers.edu does not exist (in reply to MAIL FROM command)

Modify /etc/postfix/main.cf by adding line

canonical_maps = hash:/etc/postfix/canonical

Create a new file, /etc/postfix/canonical with the following content:

@node18.rutgers.edu    @capone.rutgers.edu
@unisys18.rutgers.edu  @capone.rutgers.edu

Rebuild canonical maps and reload the server:

postmap /etc/postfix/canonical
/etc/init.d/postfix reload

If you send email again, it should be delivered fine and appear as coming from User_Name@capone.rutgers.edu. Don't try to respond to it as it won't be delivered to the private network.
Comment out the line in /etc/postfix/main.cf

#canonical_maps = hash:/etc/postfix/canonical

otherwise, email for local destinations will end up at capone. Reload postfix server again.

Header Filtering.
Modify /etc/postfix/main.cf file by including an extra line with

header_checks = regexp:/etc/postfix/bad_headers

Reload the postfix as you always do after modifying /etc/postfix/main.cf:

/etc/init.d/postfix reload

Create a new file, /etc/postfix/bad_headers with the following content:

/^Subject:(.*)Mortgage Low Rates/                                       REJECT Mortgage Rates
/^Subject:(.*)[Vv]iagra/                                                REJECT Viagra
/^Subject:(.*)[Ss]ildenalfil/                                           REJECT You meant the v-word.
/^Subject:(.*)[Cc]itrate/                                               REJECT You meant the v-word.
/^Subject:(.*)[Cc]ialis/                                                REJECT c_ialis.
/^Subject:(.*)[Ee]nzyte/                                                REJECT e_nzyte.
/^Content\-Transfer\-Encoding:(.*)base64$/                              REJECT base_64

Try to send emails to yourself at the node with the following subjects: 'Viagra', 'Mortgage Low Rates', 'Cialis' and notice how emails bounce off.

Body content filtering
Modify /etc/postfix/main.cf file by including an extra line with

body_checks =  regexp:/etc/postfix/bad_content

Reload the postfix as you always do after modifying /etc/postfix/main.cf:

/etc/init.d/postfix reload

Create a new file, /etc/postfix/bad_content with the following content:

/Nude Celebrities/                                              REJECT  Nude celebrities
/FREE MEMBERSHIP/                                               REJECT  Free membership

Try to send emails to yourself containing 'Nude Celebrities' and 'FREE MEMBERSHIP' in the text and watch for error messages.

Reject email from hosts with unresolvable names.
Modify /etc/postfix/main.cf file by including extra two lines with

smtpd_helo_required = yes
smtpd_helo_restrictions = reject_unknown_hostname

Reload the postfix. Email to youself at the node machine. You should get a bounce off error similar to the following:

[Mail not sent: : Helo command rejected: Host not found]

Since we don't have a local DNS, your desktop machine is unresolvable. Comment out these lines in /etc/postfix/main.cf, otherwise, you won't be able to send emails from your desktop.

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