If I want to inform ALL members of a Site with a specific message - there is no (official) posibility for this.
But the watching system is either

• overloading the members with notifications we cannot stop ( without perhaps making the categories private) until the watchers have enough and stop this or
• reaching nobody , because of the watchers has stopped this traffic personnaly on the accounts.

I wish a specific category ("mesage-to-all-watchers") or page-only :

• which CANNOT be disabled from the watchers
• which is only editable by the Master admin ! ( and not the other admins!)
• which is enabled for comments /discuss - only for the MA !
• which is sending every MA-comment as emails to all members ( watching this one page/category only by automatic)

I made by chance a mistake on the handbook - enabling site specific profiles and had to inform most of the embers of this fact - and deleteing it again.
I did it with such watching page:
Handbook:Message to all watchers

Edit: changed the link to the specific category…