Network Port: 587
Network Port Reference Guide
Registered Service Name
SMTP Message Submission
Transport Protocol
TCP
Functional Overview
Port 587 is the standard port for modern email client submission (MUA to MTA) using STARTTLS encryption.
Security Risks & Vulnerabilities
Relies on clients upgrading connection via STARTTLS. Insecure configurations can fall back to cleartext if TLS negotiation fails.
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 587/tcp
Block Command
sudo ufw deny 587/tcp
iptables Firewall Rules
Allow Command
sudo iptables -A INPUT -p tcp --dport 587 -j ACCEPT
Block Command
sudo iptables -A INPUT -p tcp --dport 587 -j DROP