Port 993 – IMAPS Protocol Specification

Technical analysis, security advisories, vulnerability mitigation, and firewall syntax for TCP/UDP port 993 (IMAPS).

Port Number 993

Transport Protocol TCP

Port Range Type Well-Known (0-1023)

Default Status Restricted / LAN

Service Description & Architectural Context

Internet Message Access Protocol over SSL/TLS for secure mailbox sync.

IANA / RFC Designation:

Port 993 is assigned to IMAPS 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

Standard secure email client endpoint. Verify TLS 1.2+ negotiation.

Hardening Recommendations:

Do not expose port 993 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 :993 or netstat -ano | findstr :993.

Firewall Rule Snippets for Port 993

UFW (Ubuntu / Debian Linux)

sudo ufw allow 993/tcp

iptables (Standard Linux Kernel)

sudo iptables -A INPUT -p tcp --dport 993 -j ACCEPT

Windows PowerShell (Defender Advanced Firewall)

New-NetFirewallRule -DisplayName "Allow Port 993" -Direction Inbound -LocalPort 993 -Protocol TCP -Action Allow

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