telnet binary package in Ubuntu Focal amd64

 The telnet command is used for interactive communication with another host
 using the TELNET protocol.
 .
 For the purpose of remote login, the present client executable should be
 depreciated in favour of an ssh-client, or in some cases with variants like
 telnet-ssl or Kerberized TELNET clients. The most important reason is that
 this implementation exchanges user name and password in clear text.
 .
 On the other hand, the present program does satisfy common use cases of
 network diagnostics, like protocol testing of SMTP services, so it can
 become handy enough.

Source package