Send message displays a Windows message box on the user's session. Use it to warn users before a reboot, ask them to log off, or tell them about a problem you are about to fix.

Select one or more sessions on the User sessions tab, then:
You can also send a message to every user on a whole server: right-click the server on the Servers tab and choose Send message to all users.
The Send message dialog opens.
The recipient line at the top of the dialog says exactly who the message will go to: a specific session, every session on a server, every session on a list of servers, and so on.
The title and body support placeholders. They are replaced just before the message is sent. Five tokens are recognized:
%computer_name% - the local computer name of the machine running Terminal Services Manager.%user_name% - the user name of the operator running Terminal Services Manager.%date% - the current date.%time% - the current time.%time_now% - the current date and time as a single string.Variable names are case-insensitive. Per-recipient tokens (recipient user, server, session ID, client name) are not supported; the message text is the same for every recipient on a multi-target send.
Click Send message to send. The dialog blocks until every send has finished. The recipient sees the message immediately. Their OK click is not reported back to Terminal Services Manager; if you need a reply, ask the user to contact you separately.
The arrow next to the Send message button offers extra actions:

Ctrl+Shift+Enter) - show the message box on your own screen to check the wording before sending.Ctrl+N) - clear the form to start a fresh message.Ctrl+Alt+Enter) - save the current title, body, and type as a preset for one-click reuse.