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Port 174 (mailq)

IANA assigns port 174 to mailq: MAILQ.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
mailq TCP MAILQ Rayan Zachariassen -
mailq UDP MAILQ Rayan Zachariassen -

Check what is listening on port 174

Linux: is anything listening on TCP 174?
sudo ss -tlnp 'sport = :174'
Linux: UDP 174
sudo ss -ulnp 'sport = :174'
Linux / macOS: which process owns the port
sudo lsof -nP -i :174
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':174 '
Windows (Command Prompt)
netstat -ano | findstr :174
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 174 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 174
From Windows
Test-NetConnection HOST -Port 174
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 174

Block port 174 in the firewall

ufw
sudo ufw deny 174/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 174 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 174 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 174' -Direction Inbound -Protocol TCP -LocalPort 174 -Action Block
ufw
sudo ufw deny 174/udp
iptables
sudo iptables -A INPUT -p udp --dport 174 -j DROP
nftables
sudo nft add rule inet filter input udp dport 174 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 174' -Direction Inbound -Protocol UDP -LocalPort 174 -Action Block

Related ports

172cl-1, cl/1173xyplex-mux175vmnet176genrad-mux

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.