The game server will be down while some hardware is swapped around. Depending on component compatibility, it's possible a new OS install will be done as well.
There is a backup server though, in case people want to play games meanwhile. To use the other server, edit Outpost2.ini, comment out the old GameServer line and add the following one:
IMPORTANT: All clients must be using the same game server to see each other's games. Hence this should only be done temporarily.
As a side note, I plan to make the outpost2.net game server the primary at some point in the future, but I'd like that change to be rolled into an updated download package so everyone switches at basically the same time.
Edit: Game server is now back up.