Send mail is one of the old and widely used mail delivery agent/Mail system.

First Please check this link to know more about Mail Server

    Configuration Of Sendmail :

1. All the sendmail configuration files are located at /etc/mail

2. Main configuration files are access, sendmail.mc and send mail.cf.

3. In this example my domain is example.com and my mail server host-name is mx.example.com  

Step1 : Install sendmail packages

#yum install sendmail*

#yum install m4  

Step2 : Configure DNS entries in forward look-up zone file

#vi /path/to/your/forward/lookup/zone/file

mx1.example.com. IN MX 10 example.com.

Save the file and exit.  

Step3 : Check for configuration errors and reload the DNS server

#named-checkzone example.com /path/to/your/forward/lookup/zone/file

#service named reload  

Step4 : All the sendmail configuration files are stored in /etc/mail and now configure relay ip address list  

Why we require this relay list?

Ans : This is because to secure your sendmail not get spam. So what ever Network/host-names you specified in this access file those networks/host-names only get access to our sendmail.

#vi /etc/mail/access  

Entries as follows.

192.168.0.0/24 RELAY

Save and exit the file  

Step5 : Now update the file to sendmail database with makemap command  

Note : After executing below command you will find access.db, this is the indication that your makemap command worked perfect and database have been updated successfully.  

Note : So if you want to relay more networks you have to edit access file.

#makemap hash access < access  

Step6 : Configure sendmail.mc file

#vi /etc/mail/sendmail.mc  

Step6(a) : Search for "confAUTH_OPTIONS" with out quotes open a new line after that and enter below entry in that line define(`confDOMAIN_NAME', 'example.com')dnl  

Caution : When using the quotes, "`" opening quote is near to escape key and "'" closing quote is at enter key.  

Step6(b) : Search for 127.0.0 line and comment that line if its not commented.

dnl #DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl    

Step6(c) : Search for LOCAL_DOMAINN with out quotes and modify the line as below from.

LOCAL_DOMAIN(`localhost.localdomain')dnl  
to

LOCAL_DOMAIN(`mx.example.com')dnl  

Step6(d) : Search for "MASQUERADE_AS" with out quotes and modify the line as below from..

dnl MASQUERADE_AS(`mydomain.com')dnl

  to   MASQUERADE_AS(`example.com')dnl

Now save the file and exit  

Step7 : Now compile sendmail.mc changes to reflect them in sendmail.cf

#m4 sendmail.mc > sendmail.cf

 Step8 : Now start/restart the sendmail service

#service sendmail restart

Step9 : Now add the sendmail service to chkconfig list to start automatically at booting times

#chkconfig sendmail on

Dovecot Configuration :  

Step1 : Install the dovecot package

#yum install dovecot  

Step2 : Search for "protocols" in /etc/dovecot.conf file and replace with below mention line.

#vi /etc/dovecot.conf

#protocols = imap imaps

Replace this with

protocols = pop3 imap imaps  

Step3 : Start the dovecot service.

#service dovecot restart  

Step4 : Now add the dovecot service to chkconfig list to start automatically at booting times

#chkconfig dovecot on  

Testing the mail server  

Step1 : Try sending mail using telnet command

#telnet mx.example.com 25

 

Server responds with: 220 mx.example.com SMTP then type HELO

HELO

Now Server responds with: 250 OK now send MAIL FROM:[email protected]

MAIL FROM:[email protected]

Now Server responds with: 250 Address Ok. Now type

RCPT TO:[email protected]

Now Server responds with: 250 user@ex ample.com OK.

now type DATA to enter mail content.

 

DATA

 

Now Server Responds (or may not): 354 Enter Mail

Enter message, then on a new line,.

exit

Now the message will be sent to [email protected].

 

Now log-in to that user and try to see the mail. #su   user$mail   Here you can see your mail.As send mail configuration is huge and depends on the requirement. Here the configuration which I have shown you is basic configuration.   Some FAQ's:  

Q. What is the port number for SMTP?

Ans : 25  

Q. What is the port number for POP3, IMAP?

Ans : 110, 143  

Q. What is present sendmail version?

Ans : 8  

Q. What are other highly used mail servers in world?

Ans : qmail, exchange etc

Do you want to find port numbers to other protocols too? Use google squared. My example is here