Port 143 – IMAP Protocol Specification

Technical analysis, security advisories, vulnerability mitigation, and firewall syntax for TCP/UDP port 143 (IMAP).

Port Number 143

Transport Protocol TCP

Port Range Type Well-Known (0-1023)

Default Status Restricted / LAN

Service Description & Architectural Context

Internet Message Access Protocol for real-time mailbox sync.

IANA / RFC Designation:

Port 143 is assigned to IMAP 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. Modern mail servers must enforce IMAPS on port 993 or STARTTLS.

Hardening Recommendations:

Do not expose port 143 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 :143 or netstat -ano | findstr :143.

Firewall Rule Snippets for Port 143

UFW (Ubuntu / Debian Linux)

sudo ufw allow 143/tcp

iptables (Standard Linux Kernel)

sudo iptables -A INPUT -p tcp --dport 143 -j ACCEPT

Windows PowerShell (Defender Advanced Firewall)

New-NetFirewallRule -DisplayName "Allow Port 143" -Direction Inbound -LocalPort 143 -Protocol TCP -Action Allow

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