You need to tell everyone on the network the same thing at the same time. A server is going down at 5 pm, the office is closing early, or a maintenance window starts in ten minutes. You want one pop-up on every screen, not a slow walk from desk to desk.
The manual way: msg.exe
net send was removed after Windows XP and Server 2003, so it is gone from every supported version of Windows. The built-in replacement is msg.exe. It sends a message to the terminal-services sessions on a single host:
msg * /server:PC1 Reboot at 5pm
That * covers all sessions on PC1, but only on PC1. To reach the whole network you call msg.exe once per host (usually in a loop over a list), and it gives you nothing else: no window to type in, no saved list of machines, no message types, and no record of what you sent.
The faster way: LanSend
LanSend sends one message to every checked computer at once. There is nothing to install on the recipients, and it uses the same Windows messaging channel as msg.exe, so you need network reach to each target and administrative rights on it by default — configurable via Terminal Services permissions (see Enable Message Sending for Standard Users).
- Build or open your computer list. Add machines from the Computers menu (Add computer, Add multiple computers..., or Add computers from...), or open a saved list with File > Open.
- Select every machine. From the Computers menu, click Check all. To leave a few out, uncheck them in the list.
- Pick the message type. In the composer, choose from the type combo: None, Info, Warning, or Error. Info, Warning, and Error each show the matching Windows icon and sound.
- Write the title and body. Fill in the title field and the message body. You can drop in variables that expand to the sender's values, for example
%computer_name%,%user_name%, and%time_now%. - Set the session scope. In the Sessions: dropdown choose All sessions, Active, Logged-on, or Console. All sessions reaches everyone signed in to each machine.
- Set an auto-close timeout (optional). Tick Close message after, then set a value from 1 to 60 and a unit of seconds, minutes, or hours. Leave it unticked and the pop-up stays until the user clicks OK.
- Send it. Click Send message. The same pop-up appears on every checked computer.
Want to see it first? Click Preview message to show the pop-up on your own screen with the same type, title, and timeout before it goes out.
Save it as a preset for next time
Recurring announcements do not need retyping. Write the message once, then choose Message > Add message to presets to save its name, title, body, and type. Next time, open it from the Presets menu or the presets button (the menu icon next to the message body) and it fills the title, body, and type for you. LanSend ships with ready categories such as Maintenance & Updates and Emergency & Critical, so a "Scheduled Maintenance" or "Planned Server Restart" note is one click away.
What a broadcast does, and does not do
A LanSend message notifies people. It does not restart, lock, or log anyone off, and it cannot force an action. Use it to warn users so they can save their work and act on their own.