Port 109: POP2
Port 109 is POP2, an early version of the Post Office Protocol for downloading mail. It was superseded by POP3 on port 110 decades ago and is essentially unused today.
| Port number | 109 |
|---|---|
| Service | Post Office Protocol v2 |
| Protocol | TCP |
| Category | |
| Default encryption | No |
How do I check whether port 109 is open?
Port 109 carries TCP, so a connection either completes its handshake or it does not, which makes the check definitive.
| Question | Command | What to know |
|---|---|---|
| Is it open on a remote host? | nc -vz example.com 109 | A TCP handshake either completes or it does not, so netcat gives a definitive answer in one line. |
| Same check on Windows | Test-NetConnection example.com -Port 109 | Built into PowerShell. TcpTestSucceeded in the output is the answer; telnet is not installed by default on modern Windows. |
| What is listening locally? | ss -tlnp | grep ':109 ' | Lists the process bound to port 109 on Linux. On macOS use lsof -nP -iTCP:109 -sTCP:LISTEN, on Windows netstat -ano | findstr :109 |
Replace example.com with the host you are testing. A blocked port and a port with nothing listening on it look identical from the outside, so if a service should be running, check locally before blaming the firewall.
Frequently asked questions
What is port 109 used for?
Port 109 is POP2, an early version of the Post Office Protocol for downloading mail. It was superseded by POP3 on port 110 decades ago and is essentially unused today.
Is port 109 TCP or UDP?
Port 109 (POP2) uses TCP.
Is port 109 secure?
Port 109 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 109 on my firewall?
Only if you specifically need POP2. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.