Telnet (the command) is still how I discover who the admin is for any given mail server. Random OSes don't come with nc.

  telnet mail.foo.com 25
  Connected to mail.foo.com port 25.
  EHLO mail.foo.com
  250-mail.foo.com Hello [172.16.0.5]
  MAIL FROM: 
  250 2.1.0 Sender OK
  RCPT TO: , , , 
  250 2.1.5 Recipient OK
  DATA
  354 Start mail input; end with .
  Subject: looking for mail admin
  
   Hello! I'm Blahblah, I really need to reach the mail admin. Who are you?? How can I reach you?
  
  .

Is putty still used significantly in the windows world? Is there something better these days?

https://github.com/microsoft/terminal