It is a Linux mail server based on the protocols:

• SMTP (Simple Mail Transfer Protocol)
• POP3 (Post Office Protocol)
• IMAP (Internet Message Access Protocol)

Operating system: Debian 9 64bit

No-ip

Thuderbird application

• Packages:
• Postfix
• Spamassassin
• Letsencrypt
• Bsd-mailx
• Procmail
• dovecot-imapd, dovecot-pop3d, dovecot-lmtpd

Mail server with domain: wtmail.hopto.org

Automated script to install an encrypted mail server with a spam tray and also accept the three operating modes:

• Online mode: direct access to emails
• Offline mode: synchronize the tray by taking emails from the mail server
• Disconnected mode: allow users to keep local copies of emails

1. Ask for the dynamic ip domain in No-ip (https://www.noip.com/)

2. Configure the DNS record update in No-ip

3. Download and demonize the noip2 script to start at system boot

    wget https://www.noip.com/client/linux/noip-duc-linux.tar.gz
    tar -xf noip-duc-linux.tar.gz
    cd noip-2.1.9-1/
    make
    make install
    cp debian.noip2.sh /etc/init.d/debian.noip2.sh 
    ln -s /etc/init.d/debian.noip2.sh /etc/rc0.d/K01debian.noip2.sh
    ln -s /etc/init.d/debian.noip2.sh /etc/rc1.d/K01debian.noip2.sh  
    ln -s /etc/init.d/debian.noip2.sh /etc/rc2.d/K01debian.noip2.sh  
    ln -s /etc/init.d/debian.noip2.sh /etc/rc3.d/K01debian.noip2.sh  
    ln -s /etc/init.d/debian.noip2.sh /etc/rc4.d/K01debian.noip2.sh
    ln -s /etc/init.d/debian.noip2.sh /etc/rc5.d/S01debian.noip2.sh
    ln -s /etc/init.d/debian.noip2.sh /etc/rc6.d/K01debian.noip2.sh  
    chmod 755 debian.noip2.sh
    systemctl start postfix
    systemctl enable postfix
   

1. Set private ip for the mail server
2. Open NAT port to receive requests

1. Installl postfix:

    apt-get install postfix
   

1. Install procmail:

    apt-get install procmail
   

2. Configure Postfix in /etc/postfix/main.cf

     echo "myhostname = $host_name" >> /etc/postfix/main.cf
     echo "mydomain = $host_name" >> /etc/postfix/main.cf
     echo 'myorigin = $mydomain' >> /etc/postfix/main.cf
     echo 'mydestination= $myhostname, localhost.$mydomain,$mydomain,mail.$mydomain,www.$mydomain' >> /etc/postfix/main.cf
     echo 'mail_spool_directory = /var/spool/mail' >> /etc/postfix/main.cf
     echo 'mynetworks = 127.0.0.0/8, 192.168.1.0/24' >> /etc/postfix/main.cf
     echo 'inet_protocols = ipv4' >> /etc/postfix/main.cf
     systemctl reload postfix
     postfix check
   

1. Implement the SPAM tray using "spamassassin"

     apt-get install spamassassin
     systemctl start spamassassin
     systemctl enable spamassassin
   

2. Integrate in postfix and restart it

   echo ':0 hbfw' >> /etc/procmailrc
   echo '| /usr/bin/spamc' >> /etc/procmailrc
   echo 'mailbox_command = /usr/bin/procmail' >> /etc/postfix/main.cf
   systemctl restart postfix
   

1. Secure the SMTP connection through TLS (Generating the certificate and the key using openssl)

    cd /etc/postfix
    openssl genrsa -des3 -out mail.key
    openssl req -new -key mail.key -out mail.csr
    cp mail.key mail.key.original
    openssl rsa -in mail.key.original -out mail_secure.key
    openssl x509 -req -days 365 -in mail_secure.csr -signkey mail_secure.key -out mail_secure.crt
   

2. Add the TLS options to the Postfix configuration file /etc/postfix/main.cf

    cp mail_secure.crt /etc/postfix/
    cp mail_secure.key /etc/postfix/
    echo 'smtpd_use_tls = yes' >> /etc/postfix/main.cf
    echo 'smtpd_tls_cert_file = /etc/postfix/mail_secure.crt' >> /etc/postfix/main.cf
    echo 'smtpd_tls_key_file = /etc/postfix/mail_secure.key' >> /etc/postfix/main.cf
    echo 'smtp_tls_security_level = may' >> /etc/postfix/main.cf
    systemctl restart postfix
   

3. Encrypt traffic using the free SSL certificate provider (Let's Encrypt)

    letsencrypt certonly --standalone -d "$host_name"
    postconf -e "mtpd_tls_cert_file = /etc/letsencrypt/live/$host_name/fullchain.pem"
    postconf -e "smtpd_tls_key_file = /etc/letsencrypt/live/$host_name/privkey.pem"
    systemctl restart postfix
   

1. Install Dovecot to integrate POP3 and IMAP

    apt-get install dovecot-imapd dovecot-pop3d dovecot-lmtpd
   

2. Configure Dovecot in /etc/dovecot/conf.d/dovecot.conf

    systemctl start dovecot
    systemctl enable dovecot
    echo "protocols =  imap pop3 lmtp" >> /etc/dovecot/dovecot.conf
    echo "listen = *, ::" >> /etc/dovecot/dovecot.conf
    echo "userdb {" >> /etc/dovecot/dovecot.conf
    echo "driver = passwd" >> /etc/dovecot/dovecot.conf
    echo "}" >> /etc/dovecot/dovecot.conf
    echo "passdb {" >> /etc/dovecot/dovecot.conf
    echo "driver = passwd" >> /etc/dovecot/dovecot.conf
    echo "}" >> /etc/dovecot/dovecot.conf
   

3. Modify generic Dovecot SSL certificates to Let's Encrypt certificates

    echo "mail_location = mbox:~/mail:INBOX=/var/mail/%u" >> /etc/dovecot/conf.d/10-main.conf
    echo "ssl_cert = </etc/letsencrypt/live/$host_name/fullchain.pem" >>  /etc/dovecot/conf.d/10-ssl.conf
    echo "ssl_key = </etc/letsencrypt/live/$host_name/privkey.pem" >> /etc/dovecot/conf.d/10-ssl.conf
    echo "ssl = yes" >> /etc/dovecot/conf.d/10-ssl.conf
   

1. Enable MX in No-ip

1. Text your email server