IMAP
What is Port 143?
Port 143 is the default port for the Internet Message Access Protocol (IMAP), an email retrieval protocol defined in RFC 9051 (IMAP4rev2). Unlike POP3 which downloads emails to a single device, IMAP synchronizes email across multiple devices by keeping messages on the server. IMAP supports folders, message flags, server-side search, and partial message retrieval, making it far more versatile than POP3. Developed in 1986 by Mark Crispin at Stanford University, IMAP has become the dominant email access protocol for personal and enterprise use. It allows users to read, organize, and manage email from any device — phone, tablet, laptop, or desktop — while maintaining a consistent view. Most modern email providers including Gmail, Outlook, and Yahoo Mail support IMAP.
Common Uses
- Multi-device email synchronization
- Server-side email organization and folder management
- Mobile email client access
- Enterprise email systems with shared mailboxes
Technical Details
Copy-paste commands to check port 143 (IMAP) from your terminal
Test connectivity
nc -zv example.com 143
curl -v --max-time 5 http://example.com:143/
telnet example.com 143
nmap -p 143 -sV example.com
(echo > /dev/tcp/example.com/143) 2>/dev/null && echo "open" || echo "closed"
Open port in firewall
sudo ufw allow 143/tcp
sudo iptables -A INPUT -p tcp --dport 143 -j ACCEPT
sudo firewall-cmd --permanent --add-port=143/tcp && sudo firewall-cmd --reload
Security Considerations
IMAP on port 143 transmits data in plaintext by default. Always use IMAPS (port 993) with TLS encryption or enable STARTTLS on port 143. IMAP accounts are targeted by brute force attacks and credential stuffing. Implement rate limiting, account lockout policies, and multi-factor authentication. Monitor for unauthorized access patterns.
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