macOS 10.13: Telnet is gone.. Use NC

With the demise of telnet in macOS 10.13 High Sierra it is recommended we use the nc command.

Here is an example os the usage:

nc -z 192.168.110.220 8443

The -z flag can be used to tell nc to report open ports, rather than initiate a connection

You can also test a range:

nc -z 192.168.110.220 1-8443

View the man page for nc: 

man nc