POP3
What is Port 110?
Port 110 is the default port for the Post Office Protocol version 3 (POP3), an email retrieval protocol defined in RFC 1939. POP3 allows email clients to download messages from a mail server to the local device, typically removing them from the server afterward. This download-and-delete model made POP3 ideal for users with limited server storage or slow connections, as it allowed offline access to email. POP3 was the dominant email access protocol before IMAP gained popularity. It operates in a simple transaction model: the client authenticates, lists messages, retrieves desired messages, and optionally deletes them. Many legacy email systems and basic email clients still support POP3. It remains useful for single-device email access and archiving scenarios.
Common Uses
- Downloading email to a single desktop client
- Offline email access and local archiving
- Legacy email system compatibility
- Simple email retrieval for automated processing
Technical Details
Copy-paste commands to check port 110 (POP3) from your terminal
Test connectivity
nc -zv example.com 110
curl -v --max-time 5 http://example.com:110/
telnet example.com 110
nmap -p 110 -sV example.com
(echo > /dev/tcp/example.com/110) 2>/dev/null && echo "open" || echo "closed"
Open port in firewall
sudo ufw allow 110/tcp
sudo iptables -A INPUT -p tcp --dport 110 -j ACCEPT
sudo firewall-cmd --permanent --add-port=110/tcp && sudo firewall-cmd --reload
Security Considerations
POP3 on port 110 transmits usernames, passwords, and email content in plaintext. Use POP3S (port 995) with TLS encryption instead. POP3 is vulnerable to credential sniffing, brute force attacks, and session hijacking. If you must use port 110, ensure STLS (STARTTLS) is supported and enforced. Better yet, migrate to IMAP with TLS for multi-device access.
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