I upgraded to Windows 10 (from 8.1) begin of last week and since Outlook 2013 on my system cannot connect to our company's Exchange server anymore, at least not while on the "internet". If I'm inside the company network or I connect via VPN everything works fine. Before that I was able to connect from "anywhere".

The network and firewall people claim, they haven't changed anything. It might of course simply be a stupid coincidence, but I think that is quite unlikely, so I suspect, that the Windows 10 upgrade brought some change in networking, connection setup, encryption, authentication or whatever that now prevents me from connecting to the Exchange server from outside our company network.

Being disconnected from Email (or requiring to always be connected via VPN) is a nuisance. Any ideas or suggestions what could cause this and how to remediate this?