Port 110 / TCP
POP3
Port 110 – POP3 Protocol Specification
Technical analysis, security advisories, vulnerability mitigation, and firewall syntax for TCP/UDP port 110 (POP3).
Port Number
110
Transport Protocol
TCP
Port Range Type
Well-Known (0-1023)
Default Status
Restricted / LAN
Service Description & Architectural Context
Post Office Protocol v3 for retrieving stored email messages.
IANA / RFC Designation:
Port 110 is assigned to POP3 under the Internet Assigned Numbers Authority (IANA) service name registry. In enterprise infrastructure and homelab setups, services listening on this port must follow the principle of least privilege.
Security Analysis & Attack Surface Assessment
Unencrypted cleartext authentication. Enforce POP3S over port 995 with TLS.
Hardening Recommendations:
- Do not expose port 110 to public WAN interfaces unless authenticated TLS or VPN wrapping is strictly enforced.
- Enforce rate-limiting using Fail2ban, CrowdSec, or cloud edge DDoS protection.
- Audit active listening sockets locally:
ss -tulpn | grep :110ornetstat -ano | findstr :110.
Firewall Rule Snippets for Port 110
UFW (Ubuntu / Debian Linux)
sudo ufw allow 110/tcp
iptables (Standard Linux Kernel)
sudo iptables -A INPUT -p tcp --dport 110 -j ACCEPT
Windows PowerShell (Defender Advanced Firewall)
New-NetFirewallRule -DisplayName "Allow Port 110" -Direction Inbound -LocalPort 110 -Protocol TCP -Action Allow