Wanting to know how email worked and then stumbling on it being mentioned next to the relevant RFCs was my first exposure! You could easily check pop3 mail over telnet, by sending all the commands by hand. HELO!
I then made my first email client, then an RFC later, and after browsing the web through telnet for a while, made my first web server!
I think I was the only one in the operations team who knew how to use telnet to check connections and existence of adresses on company and outside email servers.
As well as other low level tools to diagnose problems with Windows PCs and servers. There just weren't any gui tools like that.
During the Summer of 1997, I stayed at my university and had a job at the computer lab in the basement of the library. We had four Windows 95 PCs, four Mac Quadras, and then tons of VT terminals. I specifically remember the one at the lab assistants desk being a VT-320. Anyway, it was enough for me to telnet to BatMUD. I got all the way up to level 32 or so (and made some friends!) before I stopped playing. Man, that was a great Summer. Well ... it was great until I got cheated on but that's a whole other story. :-p
MUDding both taught me programming and pretty well wrecked my schooling, although in fairness, I didn't take college very seriously. Never finished my degree, which I now regret.
I fixed a client’s Outlook many years ago with telnet. The app just wouldn’t download email. No error.
So, with the guy looking over my shoulder, I telnet to the email server, list his messages, and discover that there’s an email with an attachment that’s too big for Outlook to handle. Read some basic info from the message so he could confirm that deleting the message was fine - deleted the message, and Outlook worked again.
Telnet was among my debugging tools for web applications.
And sending an email without line editing felt much more exciting than a dedicated mail client. Just dig the remote MX, telnet to port 25 and do it by hand. Marvelous!
I vaguely remember using telnet to debug nodes from behind load balancers. I would ssh to the load balancer ( just a freebsd box with Apache ). Then telnet from there to port 80 on one of the app servers and issue get requests (including headers) by hand to see what the loadbalancer was seeing in the responses. Very tedious, I can't remember why but i do remember a BOF literally standing behind me and forcing me to do this with telnet and not something like curl/wget.
Back in 1991 the older students showed me how to telnet to port 25 and make my "From:" email address be anything. It was funny when the person sitting next to me received an email from satan@hell.gov
My very political grandpa definitely received a few emails from the "president", along with a few email from a "government agency" following up on the emails.
I remember showing it to people on school computers circa....2008? Which was funny because nearly everything was blocked on these machines......but CMD and telnet worked fine lol. I remembered the URL by heart because of it :D
I discovered Telnet from some schlocky book [1] my parents had bought at Barnes and Noble about "Ethical Hacking" written by a guy who was later given a "Security Charlatan of the Year" award at DEF CON 20. I'd no idea it was a protocol - I thought it was just a program that let you talk directly to services like SMTP. I found netcat and friends later and thus never really got to use telnet for its intended purpose.
I hate this server. Every single time someone talks about Telnet mentions this site for past FIFTEEN or TWENTY YEARS as something novel.
ITs not obscure, not unknown or special - it's the most known talent site on earth.
It was made AFIR to show capabilities of ffmpg ASCII/ANSI renderer.
Real gems are SDF.ORG, TWENEX.ORG, or Cray 1 supercomputer Access, bbses and backdoors.
Ps. Telnet can be run and it is DAILY inside of the telecoms and one of few ways to speak with BSC, RNC, RRUS and individual basebands(even ultra fresh with 5G). All over IP/SEC and isolated networks. You MUST know if you are serious about computer business hehe
AUDIT people also loves it - you can record entire session of Chinese or Swedish engineer doing some new shit to basebands. This or logging entire screen
It was a jewel of the Internet, yes the one telnet site everyone knew (the ONE and ONLY) and I'm genuinely sad to learn it's gone--it was still there last time I tried it.
And it definitely wasn't using ffmpeg, it was bespoke hand-typed ASCII
There's something pure about text-based interfaces. No loading spinners, no JavaScript frameworks, no cookie banners. Just text.