Open a test TCP connection to a specified IP/Port
Netcat
nc mail.server.net 25
(Windows version)
Socat
socat - TCP4:www.domain.org:80
(Windows version)
Reading socat's examples page never fails to boggle my mind.
pkgmgr
is now replaced by dism.
Install telnet from command line (run it as administrator):
dism /online /Enable-Feature /FeatureName:TelnetClient
Then you can test TCP connection by:
telnet example.com 80
Just use Putty it's tiny (and has a portable app version). It lets you specify port and can use telnet which is a TCP connection. It also has other useful functions like serial connections (no hyper terminal in Windows 7), SSH, And Rlogin. It even has a RAW function that lets establish RAW TCP connections.
Also just so your aware: Telnet is included in XP, you can use it from the command line IE:
telnet mailserver.server.com 25
Which would establish a TCP connection on port 25.