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 the session.
- sessionid The ID of the session.
- @filename Identifies a file containing a list of usernames,
- sessionnames, and sessionids to send the message to.
- * Send message to all sessions on specified server.
- /SERVER:servername server to contact (default is current).
- /TIME:seconds Time delay to wait for receiver to acknowledge msg.
- /V Display information about actions being performed.
- /W Wait for response from user, useful with /V.
- message Message to send. If none specified, prompts for it
- or reads from stdin.
- C:Usersstevalyn>