How to setup mail server on centos 7

Setup mail server on centos 7

This article helps you to install and configure basic mail server on Centos 7. Here i have used Postfix for SMTP, Dovecot for POP/IMAP and Dovecot SASL for SMTP AUTH.

Before proceeding please make sure you have assigned static IP for the server and have internet connectivity for installing packages.

                                

Setup mail server on centos 7

1. Installing packages

2. Postfix configuration

3. Dovecot configuration

4. User creation

Step 1: Installing packages

Step 1 : Assign hostname for the server using the below command.

[root@hackthesec~]# hostnamectl set-hostname mail.hackthesec.co.in

Step 2 : Make a host entry with your IP in /etc/hosts file.

172.27.0.51 mail.hackthesec.co.in

Step 3 : Now start installing packages.

[root@hackthesec~]# yum -y install postfix dovecot

After package installation continue with postfix configuration.

Step 2 : Postfix configuration

First create SSL certificate for encryption.

Step 4: Follow the below steps one by one for creation.

[root@hackthesec ~]# mkdir /etc/postfix/ssl
[root@hackthesec ~]# cd /etc/postfix/ssl
[root@hackthesec ssl]# openssl genrsa -des3 -out server.key 2048
[root@hackthesec ssl]# openssl rsa -in server.key -out server.key.insecure
[root@hackthesec ssl]# mv server.key server.key.secure
[root@hackthesec ssl]# mv server.key.insecure server.key

Leave blank for A challenge password [] value in the below step.

[root@hackthesec ssl]# openssl req -new -key server.key -out server.csr
[root@hackthesec ssl]# openssl x509 -req -days 365 -in server.csr -signkey server.key -out server.crt

Step 5 : Now open /etc/postfix/main.cf file for changes.

Find and uncomment the below lines.

#inet_interfaces = localhost #---> line no 116
#mydestination = $myhostname, localhost.$mydomain, localhost #--> line no 164

and add below lines at the end of the file. change myhostname and mydomain values with yours and home_mailbox value to your desired directory. Here it will store mails in the users home directory (Eg: /home/john/mail ).

myhostname = mail.hackthesec.co.in
mydomain = hackthesec.co.in
myorigin = $mydomain
home_mailbox = mail/
mynetworks = 127.0.0.0/8
inet_interfaces = all
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
smtpd_sasl_local_domain =
smtpd_sasl_security_options = noanonymous
broken_sasl_auth_clients = yes
smtpd_sasl_auth_enable = yes
smtpd_recipient_restrictions = permit_sasl_authenticated,permit_mynetworks,reject_unauth_destination
smtp_tls_security_level = may
smtpd_tls_security_level = may
smtp_tls_note_starttls_offer = yes
smtpd_tls_loglevel = 1
smtpd_tls_key_file = /etc/postfix/ssl/server.key
smtpd_tls_cert_file = /etc/postfix/ssl/server.crt
smtpd_tls_received_header = yes
smtpd_tls_session_cache_timeout = 3600s
tls_random_source = dev:/dev/urandom

Step 6 : Open /etc/postfix/master.cf file, add the below lines after "smtp inet n – n – – smtpd" line.

submission     inet  n       -       n       -       -       smtpd
  -o syslog_name=postfix/submission
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_recipient_restrictions=permit_sasl_authenticated,reject
  -o milter_macro_daemon_name=ORIGINATING
smtps     inet  n       -       n       -       -       smtpd
  -o syslog_name=postfix/smtps
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_recipient_restrictions=permit_sasl_authenticated,reject
  -o milter_macro_daemon_name=ORIGINATING
Now check the configuration using postfix check command.
Step 7 : Now configure Dovecot SASL for SMTP Auth. Open /etc/dovecot/conf.d/10-master.conf file, find “# Postfix smtp-auth” line ( line no:95 ) and add the below lines.
# Postfix smtp-auth
unix_listener /var/spool/postfix/private/auth {mode = 0660
user = postfix
group = postfix
}

Now check the configuration using postfix check command.

Step 7 : Now configure Dovecot SASL for SMTP Auth. Open /etc/dovecot/conf.d/10-master.conf file, find "# Postfix smtp-auth" line ( line no:95 ) and add the below lines.

# Postfix smtp-auth
unix_listener /var/spool/postfix/private/auth {mode = 0660
user = postfix
group = postfix
}

Step 8 : Open /etc/dovecot/conf.d/10-auth.conf file, find "auth_mechanisms = plain" ( Line no: 100 ) and add login to the value like below.

auth_mechanisms = plain login

Step 9 : Postfix configuration is over. Now restart both postfix and dovecot services and enable auto start.

[root@mail ~]# systemctl restart postfix
[root@mail ~]# systemctl enable postfix
[root@mail ~]# systemctl restart dovecot
[root@mail ~]# systemctl enable dovecot

Step 10 : Add the firewall rules to allow 25, 587 and 465 ports.

[root@mail ~]# firewall-cmd --permanent --add-service=smtp
[root@mail ~]# firewall-cmd --permanent --add-port=587/tcp
[root@mail ~]# firewall-cmd --permanent --add-port=465/tcp
[root@mail ~]# firewall-cmd --reload

Now start testing connectivity for each ports 25,587 and 465 using telnet and make sure you are getting AUTH PLAIN LOGIN line after issuing ehlo mail.hackthesec.co.in command in telnet.

[root@mail ~]# telnet mail.hackthesec.co.in 465
Trying 172.27.0.51...
Connected to mail.hackthesec.co.in.
Escape character is '^]'.
220 mail.hackthesec.co.in ESMTP Postfix
ehlo mail.hackthesec.co.in

Step 3 : Dovecot configuration

Start configuring Dovecot.

Step 11 : Open /etc/dovecot/conf.d/10-mail.conf file, find #mail_location = (line no : 30 ) and add the same directory which is given to home_mailbox in the postfix config file ( Step 5).

mail_location = maildir:~/mail

Step 12 : Open /etc/dovecot/conf.d/20-pop3.conf file, find and uncomment the below line ( line no : 50 ).

pop3_uidl_format = %08Xu%08Xv

Step 13 : Restart dovecot service.

[root@mail ~]# systemctl restart dovecot

Step 14 : Add firewall rules to allow 110,143,993 and 995.

[root@mail ~]# firewall-cmd --permanent --add-port=110/tcp
[root@mail ~]# firewall-cmd --permanent --add-service=pop3s
[root@mail ~]# firewall-cmd --permanent --add-port=143/tcp
[root@mail ~]# firewall-cmd --permanent --add-service=imaps
[root@mail ~]# firewall-cmd --reload

Check the connectivity for the ports 110,143,993 and 995 using telnet.

Step 4 : User creation

Now create user for testing .

Step 15 : Create user with /sbin/nologin shell to restrict login access.

[root@mail ~]# useradd -m john -s /sbin/nologin
[root@mail ~]# passwd hackthesec

Mail server is ready now, Configure user in your mail client and test send/receive.

www.hackthesec.co.in