One of the ways one can test outbound or egress firewall rules is a tcp connection test.
I recently discover portquiz.net. Port Quiz is an outgoing port tester and gives connection examples for various clients, telnet, powershell, nc (netcat), curl, wget, etc… I’ll use PowerShell in my example below.
Why would you need to use this, a recent example that we had was - is that we had some SIP phone users that had some connection issues - as the first step was to see if tcp/5060 (SIP) was accessible from their soft-phones. Was it blocked by their ISP? or some other issue?
Portquiz to the rescue:
PS>Test-NetConnection -InformationLevel detailed -ComputerName portquiz.net -Port 5060
For example, SIP is blocked from this machine and they needed to check with their ISP for further troubleshooting.
Portquiz is a handy internet facing website that listens on all ports and allows for egress network testing.