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Port 209 (qmtp)

IANA assigns port 209 to qmtp: The Quick Mail Transfer Protocol.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
qmtp TCP The Quick Mail Transfer Protocol D J Bernstein -
qmtp UDP The Quick Mail Transfer Protocol D J Bernstein -

Registry dates for this port: last modified 2018-04-05.

Check what is listening on port 209

Linux: is anything listening on TCP 209?
sudo ss -tlnp 'sport = :209'
Linux: UDP 209
sudo ss -ulnp 'sport = :209'
Linux / macOS: which process owns the port
sudo lsof -nP -i :209
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':209 '
Windows (Command Prompt)
netstat -ano | findstr :209
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 209 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 209
From Windows
Test-NetConnection HOST -Port 209
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 209

Block port 209 in the firewall

ufw
sudo ufw deny 209/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 209 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 209 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 209' -Direction Inbound -Protocol TCP -LocalPort 209 -Action Block
ufw
sudo ufw deny 209/udp
iptables
sudo iptables -A INPUT -p udp --dport 209 -j DROP
nftables
sudo nft add rule inet filter input udp dport 209 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 209' -Direction Inbound -Protocol UDP -LocalPort 209 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.