What is port 110 used for?

Port 110 is the standard TCP port used for POP3 (Unencrypted). It is commonly used by Legacy Dovecot, Courier. Legacy Post Office Protocol transferring authentication credentials and email in plaintext.

How do I check if port 110 is open?

Enter your public IP or hostname into the scanner tool and click Check. A sub-second raw TCP socket handshake will be initiated from our edge server to port 110 on your target. If the 3-way handshake finishes with SYN-ACK, the port is OPEN. If an RST packet is returned, the host is reachable but the port is CLOSED. If packets time out without response, the port is FILTERED by an ISP or firewall.

Is port 110 safe to expose to the public internet?

Exposing port 110 carries elevated security risks (High risk). Transmits usernames and passwords unencrypted. Migrate to secure POP3S (port 995) or IMAPS (port 993). For remote services, consider placing them behind a secure VPN (such as WireGuard or Tailscale) or restricting inbound access with strict IP firewall rules.

Why does port 110 show as closed or filtered?

If port 110 reports CLOSED or FILTERED, confirm that: 1) Your service is actively running and bound to 0.0.0.0 (not just localhost/127.0.0.1); 2) Your router has a port forwarding rule directing external port 110 to your machine's local IP; 3) Your operating system firewall (Windows Defender Firewall, ufw, or iptables) allows incoming connections on port 110.