Network Port: 25
Network Port Reference Guide
Registered Service Name
SMTP (Simple Mail Transfer)
Transport Protocol
TCP
Functional Overview
Port 25 is the default port for routing emails between mail servers (MTA to MTA routing).
Security Risks & Vulnerabilities
Vulnerable to spam propagation, mail spoofing, and open relay exploits. Cloud providers often block outbound port 25 traffic to prevent abuse.
How to audit network port status
1. Scan Open Ports: Use our Port Scanner utility to verify if this port is actively listening on your host.
2. Verify Encryption: Audit the service layer to confirm SSL/TLS is protecting transmission payload.
3. Hardening Rules: Apply the firewall instructions below to shut down unauthorized inbound ports.
UFW Firewall Rules
Allow Command
sudo ufw allow 25/tcp
Block Command
sudo ufw deny 25/tcp
iptables Firewall Rules
Allow Command
sudo iptables -A INPUT -p tcp --dport 25 -j ACCEPT
Block Command
sudo iptables -A INPUT -p tcp --dport 25 -j DROP