2. Postfix Mail Server Postfix is used frequently and handle thousands of messages. compatible with sendmail at command level. high performance program easier- to use, replacement for sendmail. easy to configure postfix as compared to sendmail. syntax of defining mail relay host: o Postfix : relay.example.com simple configuration of postfix compared to sendmail as it need not any macro processor to generate or modify configuration files.

3. Configuration of postfix Postfix is verified for installation as follow [root#]rpmquery –qa|grep postfix. If postfix is not installed then its installation as follows [root#]rpm -ivh postfix(name of file) Where name of the file is the version of postfix packages

4. Postfix primary configuration file is /etc/postfix/main.cf. in these file, there is need to make changes as follow: A) my domain variable specifies the domain name of user: mydomainname=example.com B) myhostname is a variable which identifies the local machine’s fully qual domain name myhostname=tyit.example.com C) myorigin variable identifies the domain name myorigin = $mydomain

5. D)My destination variable tells the postfix what addresses it should delivered My destination = $myhostname, localhost,$mydomain

6. User needs aliases for postfix, postmaster & root so that mail sent to are received to real person. To achieve these, the following entries /etc/aliases: #vi /etc/aliases Postfix : root Postmaster: root Root:john The alias database using postfix’s new aliases command is regenerated as /etc/aliases was modified. the common is as shown below: #newaliases.

7. Finally the daemon of postfix is stared as shown below: #services postfix start Starting postfix:[ok] Postfix s enabled on boot as follow: #chkconfig postfix on

8. To handle postfix log message user needs to modify the syslog configuration file add following entries: #vi /etc/syslog.conf Mail.*mail/var/log/maillog

9. Mail.err/var/log/mail.err Where /etc/syslog.conf is the file which control the system log To bring changes these change into effect, there is need to restart or start the services of syslog as follow: [root#]service syslog restart.

10. Running Postfix behind a firewall If system is not connected to internet on which postfix is configured or configure as a firewall or gateway, postfix will simply handover locally generated email to relay host. This relay host must be configured to relay to the respective receiver. for the configuration, following 2 lines are added in /etc/postfixmain.cf relayhost =mailhost $mydomain disable_DNS_lookups = yes IP address of the relay host can also be specified as follow: relayhost =192.168.166.10 Finally the service of postfix is restarted as follow: [root#]service postfix restart Stopping postfix [ok] Starting postfix[ok]

11. Running postfix on a mail host User can create a mail host that handles the incoming mail for the system The configuration of mail host assumes that the relay host, named tyit.example.com is the only of entry for all email traffic User need to set the following configuration variables on tyit.example.com: $myhostname $mydomain $myorigin $mydestination Tyit.example.com need to be told for which system it can relay mail. doing this involves setting 2 additional configuration variable as shown in example below. $ mynetwork=192.168.166.10 $relaydomains=example.com Mynetwork defines a list of trusted client, i.e. the list of client that postfixwill allow to relay mail. $ relaydomains defines the destination to which postfix will relay mail.

12. SERVING EMAIL WITH POP3 AND IMAP Suppose windows system used as desktop n/w client ordinarily do not have an MTA of theirs own.Then such system requires email access using IMAP & POP. A user can install both at a time i.e. IMAP & POP but can use only one at a time. Setting up IMAP server require the following :

13. (i) The IMAP implementation configuration is done with the help of dovecot IMAP sever. (ii) Dovecot has many features like support POP3 & IMAP which simplify initial setup & on going maintenance it mean, If user is configured IMAP server, he will get POP3 unless he disable the POP 3 services.

14. (iii) Dovecot also support POP3 & IMAP, which work for authentication & data exchange process. (iv) To configure any of the service it is necessary to check whether it is installed or not. Command to check whether Dovecot is installed is as follows: [root#]rpmquery -qa|grep dovecot

15. (v) Configuring Dovecot : If necessary package is installed,then configure the dovecot at the boot time. [root#]chkconfig dovecot ON

16. MAINTAINING E-MAIL SECURITY E-mail security is always a privacy issue even if the user is not mailing credit card number or corporate secrets. using S/MIME for security is only one of many steps to take to protect the integrity of users E-mail. There are some most comm0n vulnerabilities that can affect E-mail security :

17. (1) Protecting against Eavesdropping : (a) Because of store and forward Technique the users msg goes not only through one computer. (b) There are more possibilities that cracker can easily attack the users mail using a packet sniffer program to intercept passing mail messages. (2) Using encryption : (a)cryptography enables users message to be encrypted. So that sender & receiver can encrypt & transmit safely.

18. (b) Best way to encrypt data is to use digital signature. (3) Using Firewall: (a) User should set up a firewall to protect the network while receiving mail from people outside the network. (b) The firewall is a computer that prevent unauthorized data from reaching the n/w.

19. (4) Prevent being bombed, spammed or spoofed: (a) Bombing : it happen when someone continually or maliciously send data. (b) spamming : A spammer send non-reqd email to many user. (c) Spoofing : it happens when someone sends email from a false address.

20. 5) SMTP should be dealt with care : (a) Use of a dedicated mail servers keep the no. of computers vulnerable to SMTP based attack to a least. (b) Network should have only or few centralized email servers, depending on the size of users organization. (c) Allow only SMTP connection that come from outside user firewall to get those few central email servers.