Following URLs need to be whitelisted in the firewall :
speechexec.com
speechlive.com
blob.core.windows.net
livebroker.speechexec.com
stspeechidb2cuiweu.blob.core.windows.net
speechid.b2clogin.com
Furthermore if a GeoIP Filtering service is used, the following countries need to be unblocked:
Netherlands
Ireland