All ports
Port25/UDP
smtpPort
25
Protocol
UDP
Category
Well-Known
Service
smtp
What is port 25?
Port 25/UDP is a Well-Known port, assigned by IANA for widely recognized services. It is associated with the smtp service.
Simple Mail Transfer
Useful commands
nmapnmap -p 25 -sV example.comnetcatnc -zv example.com 25curlcurl -v http://example.com:25/telnettelnet example.com 25bash(echo > /dev/udp/example.com/25) 2>/dev/nullFirewall commands
UFWAllow
sudo ufw allow 25/udpDeny
sudo ufw deny 25/udpiptablesAllow
sudo iptables -A INPUT -p udp --dport 25 -j ACCEPTDeny
sudo iptables -D INPUT -p udp --dport 25 -j ACCEPTfirewalldAllow
sudo firewall-cmd --permanent --add-port=25/udpWindowsAllow
netsh advfirewall firewall add rule name="Open Port 25" dir=in action=allow protocol=UDP localport=25Security Risks
- Open relay used for spam
- Email spoofing
- Brute force attacks against email accounts
- Information disclosure in email headers
Frequently Asked Questions
What service runs on port 25/UDP?
Port 25/UDP is associated with the smtp service. Simple Mail Transfer
Is it safe to expose port 25 to the Internet?
It depends on the service and configuration. Port 25 (smtp) is a Well-Known port. If you need to expose it, keep the service updated, use strong authentication, and configure a firewall. It's always recommended to restrict access by IP when possible.
How do I check if port 25 is open?
You can use nmap: `nmap -p 25 -sV example.com`, netcat: `nc -zv example.com 25`, or the bash command: `(echo > /dev/udp/example.com/25) 2>/dev/null && echo "Open" || echo "Closed"`.
How do I open or close port 25 on my firewall?
On Linux with UFW: `sudo ufw allow 25/udp` (open) or `sudo ufw deny 25/udp` (close). With iptables: `sudo iptables -A INPUT -p udp --dport 25 -j ACCEPT`. On Windows: `netsh advfirewall firewall add rule name="Open Port 25" dir=in action=allow protocol=UDP localport=25`.
What applications and services use port 25?
Port 25/UDP is used by the smtp service. Specific uses depend on the software and configuration. Check our related tools section for more information.