- Require TLS and authenticated submission.
- Make sure the server is not an open relay.
- Publish SPF, DKIM and DMARC for the domain.
Port 109: Post Office Protocol - Version 2
Port 109 is assigned by IANA to pop2 (Post Office Protocol - Version 2).
109
How pop2 works
EmailMail servers hand messages to each other over port 109, one hop at a time, until the recipient's server.
- Transport
- TCP · UDP
- Exposure risk
- not rated depends on the program listening
- Encryption
- Unknownnot stated by the registry
- IANA status
- Assigned1 registered service
- Range
- Well-known (0-1023)
- Category
Is port 109 dangerous?
We have no specific security note for port 109. Its risk depends on the program actually listening on it. General advice for email services:
IANA registry entries for port 109
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| pop2 | 109 | TCP, UDP | Post Office Protocol - Version 2 | - | - |
// source: IANA service name and port number registry
Which program uses port 109, and is it reachable?
Linux
sudo ss -ltnup 'sport = :109' # process listening on 109
sudo lsof -nP -i :109macOS
sudo lsof -nP -i :109
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 109 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 109 netstat -ano | findstr :109
From another machine
nmap -p 109 -sV <host> sudo nmap -sU -p 109 <host> nc -zv <host> 109
Block it in the firewall
sudo ufw deny 109/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 109" -Direction Inbound -LocalPort 109 -Protocol TCP -Action Block # Windows
What is port 109 used for?
Port 109 is assigned by IANA to pop2 (Post Office Protocol - Version 2).
Is port 109 TCP or UDP?
Port 109 is registered for TCP and UDP.
Is it safe to open port 109?
It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Require TLS and authenticated submission.
How do I check if port 109 is open?
On Linux run "ss -ltnup 'sport = :109'", on macOS "lsof -nP -i :109", and on Windows "netstat -ano | findstr :109" to see the local process. From another machine, "nmap -p 109 <host>" shows whether it is reachable.