Port 110: POP3
TCP 110 is the port for Post Office Protocol v3. Prefer 995 only and close 110.
| Service | Post Office Protocol v3 |
|---|---|
| Protocol | TCP |
| Exposure risk | Medium: expose with care |
| Secure alternative | POP3S (port 995) |
| Range | Well-known (0–1023): binding needs root/admin on Unix |
What port 110 does
Mail clients download messages from a mailbox server with POP3. Plain POP3 can upgrade with STLS, but credentials are exposed if the client does not insist on it.
Should port 110 be open?
Prefer 995 only and close 110. Where you can, use POP3S (port 995) instead.
Find what's listening on port 110
- Linux:
sudo ss -tulpn | grep :110 - macOS:
sudo lsof -nP -i :110 - Windows:
netstat -ano | findstr :110, then look up the PID in Task Manager.
Open or block it in a firewall
- ufw:
sudo ufw allow 110/tcp(ordeny) - firewalld:
sudo firewall-cmd --add-port=110/tcp --permanent && sudo firewall-cmd --reload - Windows:
New-NetFirewallRule -DisplayName "Port 110" -Direction Inbound -Protocol TCP -LocalPort 110 -Action Allow
Port assignment per the IANA Service Name and Transport Protocol Port Number Registry. Test several ports at once with the port scanner, or any port with the open port checker.
Questions about port 110
What is port 110 used for?
Post Office Protocol v3. Mail clients download messages from a mailbox server with POP3. Plain POP3 can upgrade with STLS, but credentials are exposed if the client does not insist on it.
Is port 110 TCP or UDP?
TCP. POP3 uses TCP port 110.
Is it safe to open port 110?
Medium: expose with care. Prefer 995 only and close 110. Secure alternative: POP3S (port 995).
How do I check if port 110 is open?
Use the checker on this page: it connects to your host on TCP 110 from the internet. Locally, run
nc -vz host 110 (macOS/Linux) or Test-NetConnection host -Port 110 (PowerShell). To see what is listening on your own machine, run ss -tulpn | grep :110 (Linux) or netstat -ano | findstr :110 (Windows).