- Require TLS and authenticated submission.
- Make sure the server is not an open relay.
- Publish SPF, DKIM and DMARC for the domain.
Port 209: The Quick Mail Transfer Protocol
Port 209 is assigned by IANA to qmtp (The Quick Mail Transfer Protocol).
209
How qmtp works
EmailMail servers hand messages to each other over port 209, 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 209 dangerous?
We have no specific security note for port 209. Its risk depends on the program actually listening on it. General advice for email services:
IANA registry entries for port 209
| Service | Port | Transport | Description | Reference | Updated |
|---|---|---|---|---|---|
| qmtp | 209 | TCP, UDP | The Quick Mail Transfer Protocol | - | 2018-04-05 |
// source: IANA service name and port number registry
Which program uses port 209, and is it reachable?
Linux
sudo ss -ltnup 'sport = :209' # process listening on 209
sudo lsof -nP -i :209macOS
sudo lsof -nP -i :209
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 209 -State Listen | Select LocalAddress, OwningProcess Get-NetUDPEndpoint -LocalPort 209 netstat -ano | findstr :209
From another machine
nmap -p 209 -sV <host> sudo nmap -sU -p 209 <host> nc -zv <host> 209
Block it in the firewall
sudo ufw deny 209/tcp # Linux (ufw) New-NetFirewallRule -DisplayName "Block 209" -Direction Inbound -LocalPort 209 -Protocol TCP -Action Block # Windows
What is port 209 used for?
Port 209 is assigned by IANA to qmtp (The Quick Mail Transfer Protocol).
Is port 209 TCP or UDP?
Port 209 is registered for TCP and UDP.
Is it safe to open port 209?
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 209 is open?
On Linux run "ss -ltnup 'sport = :209'", on macOS "lsof -nP -i :209", and on Windows "netstat -ano | findstr :209" to see the local process. From another machine, "nmap -p 209 <host>" shows whether it is reachable.