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// Other services

Port 174: MAILQ

Port 174 is assigned by IANA to mailq (MAILQ).

174

How mailq works

Other services
client:174mailqresponse client:174mailqresponse

The client sends a request to port 174 and the mailq service answers.

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
Other services
01 Security

Is port 174 dangerous?

We have no specific security note for port 174. Its risk depends on the program actually listening on it. General advice for other services services:

  • Close the port if nothing on the host needs it.
  • Identify the process that listens on it (commands below) before opening it in a firewall.
  • Expose a service only to the networks that use it.
02 Registry

IANA registry entries for port 174

ServicePortTransportDescriptionReferenceUpdated
mailq 174 TCP, UDP MAILQ - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 174, and is it reachable?

Linux

sudo ss -ltnup 'sport = :174'      # process listening on 174
sudo lsof -nP -i :174

macOS

sudo lsof -nP -i :174

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 174 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 174
netstat -ano | findstr :174

From another machine

nmap -p 174 -sV <host>
sudo nmap -sU -p 174 <host>
nc -zv <host> 174

Block it in the firewall

sudo ufw deny 174/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 174" -Direction Inbound -LocalPort 174 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 174 used for?

Port 174 is assigned by IANA to mailq (MAILQ).

Is port 174 TCP or UDP?

Port 174 is registered for TCP and UDP.

Is it safe to open port 174?

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. Close the port if nothing on the host needs it.

How do I check if port 174 is open?

On Linux run "ss -ltnup 'sport = :174'", on macOS "lsof -nP -i :174", and on Windows "netstat -ano | findstr :174" to see the local process. From another machine, "nmap -p 174 <host>" shows whether it is reachable.

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