In the Launcher, in the Forum, better at both points.
What I mean:
If the server is down and you know it - throw two sentences with a timestamp our way.
If you take the server down for 15-20 min - throw two sentences with a timestamp our way.
Then not only the people ingame know if something is done, but also those that want to get in can find out that you are working on something - and that, e.g. they can try again in half an hour.
I know its extra work, but seeing something communicated, knowing about something and not having to guess is always worth the effort in satisfaction I think. After all, it also communicates that someone is working hard on something ;-)