In order for Covve to sync with your Exchange server, your Web API needs to allow access. If you can access your email and contacts through Outlook Web Access you should be fine. If you need VPN to access email, your Exchange server access is restricted and Covve will not be able to connect.
In this situation you can either:
remove the restriction or,
sync your Exchange contacts with either your iPhone or your Android and then signup to Covve from your mobile device
How can I connect Covve with my iPhone/iCloud contacts?
iCloud does not offer an open API, i.e. it does not connect with non-Apple devices and services. As such, direct sync between Covve and iCloud is not possible.
To use Covve with iCloud:
make sure your iPhone is in sync with your iCloud account and then signup to Covve from your iPhone.