Was working. Now not.
When I try to login via any address; localhost, mail.server.com, servername, with or without ?ExchClientVer=15 makes no difference. Soon as the login page loads it chances to /owa and attempting to login everytime gives a 500 error.
Googled and there's a million things I can see to try. No fucking clue what is the right thing to do. This is a new install, shouldn't be any issues but from what I can see hundreds of people the same BS.