Outlook Pro,  Outlook webclient connecting issue

When the federated authentication configuration is done in the vault settings I think you need to map the vault to a specific DNS name with the VaultDNSConfig option: Configuring Mappings Between Incoming Connections and Vaults 

So instead of connecting to server.customer.com (general address for the server) you would connect to vault.customer.com (address for the individual vault). Otherwise the add-in doesn't know from which vault on the server the authentication config should be fetched.

We'll look into adding this information to the Outlook Pro configuration guide.