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Port 143 – IMAP (Internet Message Access Protocol)

Service:

imap

Protocol:

TCP

Port:

143

Used for:

Internet Message Access Protocol for accessing and managing email on mail servers

Why It’s Open

Port 143 is used for Internet Message Access Protocol (IMAP), the standard protocol for remote email management. Unlike POP3, IMAP synchronizes messages across multiple devices by keeping them on the server. While modern implementations prefer IMAPS (port 993), many mail servers still support unencrypted IMAP for legacy compatibility.

Common Risks

  • Cleartext Communication
    Transmits credentials and emails without encryption
  • Authentication Attacks
    Vulnerable to brute force and password spraying
  • Traffic Interception
    Unencrypted sessions can be monitored
  • Version Disclosure
    Server banners reveal software information
  • Session Vulnerabilities
    Unencrypted tokens risk hijacking

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Enumeration & Testing

Check if it’s open:

Terminal window
nmap -sT -p 143

Test IMAP connection:

Terminal window
openssl s_client -connect :143 -starttls imap
Terminal window
nc -nv  143

What to Look For

CheckpointWhat it means
Unencrypted IMAPAuthentication and data exposure
Visible version infoReveals software details
Missing STARTTLSNo encryption upgrade option
Anonymous loginPotential unauthorized access

Mitigation

  • Enforce IMAPS
    Use port 993 exclusively when possible
  • Mandate STARTTLS
    Require encryption for all IMAP connections
  • Implement MFA
    Add multi‑factor authentication
  • Rate Limit Logins
    Prevent brute force attempts
  • Network Restrictions
    Limit access to required IP ranges

TL;DR

  • Standard unencrypted IMAP port
  • Should be replaced with IMAPS
  • High risk of credential attacks
  • Requires encryption and access controls

Known CVEs and Exploits