CanYouSeeMe.org - Open Port Check Tool This page will serve as a free utility for remotely verifying a port is open or closed. It will be useful for users who wish to check to see if a server is running or a firewall or ISP is blocking certain ports. Background Port 80 is the default port for http traffic. With blocked port 80 you will need to run your web server on a non-standard port in conjunction with a port 80/web redirect from No-IP.com. Port 25 is the default port for sending and receiving mail. ISPs block this port to reduce the amount of spam generated by worms on infected machines within their network. If you need to send legitimate email and your ISP blocks port 25. Consider the solutions from No-IP.com. Open Port Check tool is a free tool provided by No-IP.com . If you are having problems with your ISP blocking ports including port 25 and port 80 , No-IP has a solution.