What is port 110 used for?
Post Office Protocol: email clients download messages from the server.
Should port 110 be open?
Open only if you need it. Expose it only when required, with encryption and strong authentication, ideally limited to known IP addresses. Plain POP3 can send passwords unencrypted. Use POP3S on port 995, or IMAP.
See what is listening on port 110
# Linux
sudo ss -tlnp | grep ':110 '
# macOS
sudo lsof -nP -i TCP:110 -sTCP:LISTEN
# Windows (PowerShell)
Get-NetTCPConnection -LocalPort 110 -State ListenOpen or block port 110 in a firewall
# Ubuntu / Debian (ufw)
sudo ufw allow 110/tcp
sudo ufw deny 110/tcp
# Windows (PowerShell, as administrator)
New-NetFirewallRule -DisplayName "Port 110" -Direction Inbound -Protocol TCP -LocalPort 110 -Action AllowOn cloud servers, also open the port in the provider’s security group or network firewall. At home, a service behind a router needs a port-forwarding rule to the device’s local IP.
Test it from outside
A port can be open on the server but blocked upstream. The Port Checker connects from the internet, so it shows what the world sees. From your own machine, use nc -vz example.com 110 (macOS/Linux) or Test-NetConnection example.com -Port 110 (Windows).
Port CheckerTest whether a server accepts connections on specific ports — web (80/443), mail (25/587/993), SSH, databases or remote desktop — and see which are open, closed or filtered by a firewall.
Open the tool Frequently asked questions
What is port 110?
Post Office Protocol: email clients download messages from the server.
Is it safe to open port 110?
Open only if you need it. Expose it only when required, with encryption and strong authentication, ideally limited to known IP addresses.
How do I check if port 110 is open?
Enter your domain or public IP in the Port Checker with port 110. It tries a TCP connection from the internet and reports open, closed or filtered.