From a CMD.EXE prompt you can use the MSG command.
This replaces an older mechanism using NET SEND …
I just did this on a Windows 10 Pro system:
- C:Usersstevalyn>msg
- Send a message to a user.
- MSG {username | sessionname | sessionid | @filename | *}
- [/SERVER:servername] [/TIME:seconds] [/V] [/W] [message]
- username Identifies the specified username.
- sessionname The name of