I need to write a private message to all registered users and moderators

As an administrator, I need to write a private message to all registered users and moderators.
I went around your entire site and did not find it. But there was such a function like a long time ago? I do not remember what characters to drive into the address bar of private messages ... Please tell me.
If not.
Then tell me how can I get all user emails
from the hosting to email them. It's hard, of course.