how to broadcast message with servermsg and no need to open chat to see servermsg ?

[terse nebula]

When I use servermsg player who has don't open chat will not see a message it possible to broadcast message with no need to open chat ?

[tender folio]

Does this happen on Vanilla server?

[somber galleon]

It's happening on my server too, I have a number of mods, none of which impact chat.