You might wanna use netcat for that instead [1]. Or, for example, socat [2]. Netcat has been around for a long, long time now.

[1] nc (1) - arbitrary TCP and UDP connections and listens

[2] socat (1) - Multipurpose relay (SOcket CAT)

That's not really telnet. Yeah, it's using the same client, but the server and underlying protocol are what's relevant here.

The modern replacement for telnet used in the "probe a port" fashion is nc/netcat.