Apple decided to remove telnet and ftp from high Sierra onward. It is understandable , because they are not secure. But some of us need it for old systems, or local machines. I was able to go back into an old version of Yosemite and copy those two binaries into my current system. They are available on this page. You will need to copy them into your /usr/local/bin/ folder.
telnet and ftp for high Sierra
MD5 (telnet) = 89720c99bbdb96fdfa7f13fdc4bf0a07
MD5 (ftp) = dea942a96a3758a275b70b3f3915abda
Here High Sierra refuses the files to be copied into /usr/local/bin [or /usr/bin].
How to proceed?
Use the command “sudo”.
For example, if you downloaded telnet and ftp from the link above, they should show up in your “Downloads” folder.
Open a terminal, then enter the command as above
frank@iMac:~> sudo cp Downloads/usr/local/bin/* /usr/local/bin/
Password:
frank@iMac:~>