I can access that via vpn.
But not directly.
It might be a DNS issue that is why you couldn't access these exchange sites but you can access it via VPN and maybe your network DNS blocking you from logging in.
Changing DNS might solve the issue because in my case I couldn't access some exchange site before so try changing your DNS to Google DNS
8.8.8.8 and
8.8.4.4 or OpenDNS
208.67.222.222 and
208.67.220.220 and then check it again.