You need to specify a proxy server for the Defender Security Server to use when sending SMS tokens. You receive a message similar to the following when the proxy is not configured:
"Unable to send SMS: Failed to send OTP to dsstest on +44700000000 Session ID: 12A1A100"
A specific proxy is required.
Run the Defender Security Server service as an administrative user account. Log on as this user account and set the required proxy server in Internet Explorer.
Enhancement request 0001424 has been submitted for consideration in a future release of Defender.