Configuring the Postfix Server and Running the Server
1. Introduction
After installing Postfix, the next step is configuration and running the server so that it can properly send and receive emails using SMTP.
👉 Configuration ensures:
- Correct domain setup
- Proper mail routing
- Security and reliability
2. Main Configuration File
Postfix configuration is done in:
/etc/postfix/main.cf
👉 This file contains all core settings of the mail server.
3. Basic Configuration of Postfix
Edit the configuration file:
sudo vi /etc/postfix/main.cf
3.1 Essential Parameters
1. Hostname
myhostname = mail.example.com
- Fully qualified domain name (FQDN)
2. Domain Name
mydomain = example.com
3. Origin of Mail
myorigin = $mydomain
4. Network Interfaces
inet_interfaces = all
- Allows Postfix to listen on all network interfaces
5. Protocol
inet_protocols = ipv4
6. Destination Domains
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
- Defines domains handled locally
7. Mailbox Location
home_mailbox = Maildir/
- Stores emails in user home directory
3.2 Relay Configuration (Optional)
relayhost = [smtp.gmail.com]:587
- Used to forward emails through another SMTP server
3.3 Network Access Control
mynetworks = 127.0.0.0/8
- Defines trusted networks
4. Running the Postfix Server
4.1 Start Postfix
sudo systemctl start postfix
4.2 Enable at Boot
sudo systemctl enable postfix
4.3 Check Status
sudo systemctl status postfix
4.4 Restart / Reload
sudo systemctl restart postfix
sudo systemctl reload postfix
5. Checking Configuration
Verify Configuration
postfix check
Reload After Changes
sudo systemctl reload postfix
6. Testing the Postfix Server
6.1 Send Test Email
echo "Hello" | mail -s "Test Mail" user@localhost
6.2 Check Mail Queue
mailq
6.3 View Logs
tail -f /var/log/mail.log
7. Mail Flow in Postfix
User → Postfix → Mail Queue → SMTP → Recipient Server
8. Firewall Configuration
Allow SMTP traffic:
sudo ufw allow 25
For CentOS:
firewall-cmd --permanent --add-service=smtp
firewall-cmd --reload
9. Important Postfix Commands
| Command | Purpose |
|---|---|
postfix start | Start server |
postfix stop | Stop server |
postfix reload | Reload config |
mailq | Show mail queue |
postqueue -f | Flush queue |
10. Common Issues & Troubleshooting
| Problem | Solution |
|---|---|
| Mail not sending | Check logs |
| Port 25 blocked | Open firewall |
| Wrong hostname | Fix myhostname |
| DNS issues | Configure MX record |
11. Real-World Example
- Company mail server:
- Domain:
example.com - Postfix handles outgoing emails
- Users send emails via SMTP
- Domain:
12. Advantages of Proper Configuration
- Reliable email delivery
- Secure communication
- Efficient mail routing
- Reduced spam issues
13. Conclusion
Configuring and running Postfix is essential for building a functional email server in Linux. Proper setup of parameters, services, and security ensures smooth, secure, and reliable email communication in real-world environments.