1. How to Set Up a Mail Server on VPS Using mail.domain.com and Roundcube Webmail

   Introduction
   This guide provides a comprehensive walkthrough for setting up a mail server on your VPS, using mail.domain.com for secure email communication and Roundcube webmail for account management. We'll also cover opening and checking ports to ensure smooth operation.

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   System Requirements

   • VPS Configuration:
     • CPU: 1 core
     • RAM: 2 GB minimum
     • Storage: 20 GB minimum
   • Domain Name: Fully qualified domain like example.com.
   • DNS Management: Access to add DNS records.
   • Operating System: CentOS 7/8, AlmaLinux, Ubuntu 20.04, or Debian 11.

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   Step 1: Log in to Your VPS

   Log in using SSH:

   ssh root@your-server-ip
   

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   Step 2: Update and Prepare Your System

   Update your server packages:

   yum update -y   # CentOS/AlmaLinux  
   apt update && apt upgrade -y   # Ubuntu/Debian  
   

   Disable NetworkManager (if applicable):

   systemctl stop NetworkManager
   systemctl disable NetworkManager
   

   Enable the traditional networking service:

   systemctl enable network
   systemctl start network
   

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   Step 3: Configure DNS Records for mail.domain.com

   Update your DNS records in your domain registrar or DNS management panel:

   Record Type	Name	Value	TTL
   A	mail	Your VPS IP address	300
   MX	@ (root domain)	mail.domain.com (priority 10)	300
   TXT	@	"v=spf1 mx ~all"	300
   TXT	default._domainkey	Public DKIM key (generated later)	300
   TXT	_dmarc	"v=DMARC1; p=none"	300

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   Step 4: Install and Configure Postfix

   Install Postfix:

   yum install postfix -y   # CentOS/AlmaLinux  
   apt install postfix -y   # Ubuntu/Debian  
   

   Edit the configuration file:

   nano /etc/postfix/main.cf
   

   Update or add the following:

   myhostname = mail.domain.com
   mydomain = domain.com
   myorigin = $mydomain
   inet_interfaces = all
   inet_protocols = ipv4
   mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
   relayhost =
   mynetworks = 127.0.0.0/8 [::1]/128
   home_mailbox = Maildir/
   smtpd_tls_cert_file = /etc/ssl/certs/mail.domain.com.pem
   smtpd_tls_key_file = /etc/ssl/private/mail.domain.com.key
   smtpd_use_tls = yes
   

   Start and enable Postfix:

   systemctl start postfix
   systemctl enable postfix
   

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   Step 5: Install and Configure Dovecot

   Install Dovecot:

   yum install dovecot -y   # CentOS/AlmaLinux  
   apt install dovecot-core dovecot-imapd -y   # Ubuntu/Debian  
   

   Edit the configuration file:

   nano /etc/dovecot/dovecot.conf
   

   Add or update these lines:

   protocols = imap pop3 lmtp
   listen = *
   mail_location = maildir:~/Maildir
   ssl = required
   ssl_cert = </etc/ssl/certs/mail.domain.com.pem
   ssl_key = </etc/ssl/private/mail.domain.com.key
   

   Start and enable Dovecot:

   systemctl start dovecot
   systemctl enable dovecot
   

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   Step 6: Open Required Ports

   Mail servers require specific ports to function:

   • Port 25: SMTP (sending emails, used by servers).
   • Port 587: SMTP with STARTTLS (sending emails, used by clients).
   • Port 993: IMAP over SSL (retrieving emails).
   • Port 995: POP3 over SSL (optional).

   Steps to Open Ports

   For firewalld:

   firewall-cmd --permanent --add-service=smtp
   firewall-cmd --permanent --add-service=smtps
   firewall-cmd --permanent --add-service=imap
   firewall-cmd --permanent --add-service=imaps
   firewall-cmd --reload
   

   For UFW:

   ufw allow 25
   ufw allow 587
   ufw allow 993
   ufw allow 995
   ufw reload
   

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   Step 7: Check Open Ports

   Use online tools like MXToolbox Port Check to verify your ports are accessible.

   You can also check locally with:

   netstat -tuln | grep ':25\|:587\|:993\|:995'
   

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   Step 8: Secure the Mail Server with SSL/TLS

   Install Let's Encrypt:

   yum install certbot -y   # CentOS/AlmaLinux  
   apt install certbot -y   # Ubuntu/Debian  
   

   Generate SSL certificates:

   certbot certonly --standalone -d mail.domain.com
   

   Link the certificates:

   ln -s /etc/letsencrypt/live/mail.domain.com/fullchain.pem /etc/ssl/certs/mail.domain.com.pem
   ln -s /etc/letsencrypt/live/mail.domain.com/privkey.pem /etc/ssl/private/mail.domain.com.key
   

   Restart Postfix and Dovecot:

   systemctl restart postfix
   systemctl restart dovecot
   

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   Step 9: Install and Configure Roundcube Webmail

   Install Apache and PHP:

   yum install httpd php php-mysqlnd php-intl php-json -y   # CentOS/AlmaLinux  
   apt install apache2 php libapache2-mod-php php-mysql php-intl php-json -y   # Ubuntu/Debian  
   

   Download Roundcube:

   wget https://github.com/roundcube/roundcubemail/releases/download/1.6.1/roundcubemail-1.6.1-complete.tar.gz
   tar -xvzf roundcubemail-1.6.1-complete.tar.gz -C /var/www/html
   mv /var/www/html/roundcubemail-1.6.1 /var/www/html/roundcube
   

   Set permissions and configure Roundcube as per your mail server details.

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   Troubleshooting

   Emails Not Sending/Receiving

   • Check logs:

     tail -f /var/log/maillog   # CentOS/AlmaLinux  
     tail -f /var/log/mail.log  # Ubuntu/Debian  
     

   Port Issues

   • Use telnet to check if a port is open:

     telnet your-server-ip 25
     

   • Ensure the firewall allows the required ports.

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   FAQ

   1. How Do I Access Webmail?
      Visit http://mail.domain.com/roundcube.

   2. Can I Use Custom Email Addresses?
      Yes, create accounts using:

      useradd username
      passwd username
      

   3. What Tools Can Test My Setup?

      • MXToolbox for DNS and port verification.
      • mail-tester.com for email configuration testing.

Conclusion

This guide provides a complete roadmap to set up a mail server on your VPS with Roundcube webmail. By properly configuring Postfix, Dovecot, DNS, and webmail, you can offer a reliable and secure email solution for your hosting clients. If you encounter any issues, refer to the troubleshooting section or contact our support team.