In a Microsoft Skype for Business Server 2015 environment, you use the Skype for Business on Mac or mobile client that's in an external network to start a call with a Skype for Business client user. You may find that the value of Is From user internal or Is To user internal (depending on whether the UCWA user is the caller or callee) always shows Yes on the Call detail recording (CDR) report. It's expected that the clients should be flagged correctly as external or internal on this report.
To fix this issue, install the May 2019 cumulative update 6.0.9319.548 for Skype for Business Server 2015, Web Components Server.
After you apply this update, you have to enable this change.
Note The Set-CsPlatformServiceSettings cmdlet gives you control to enable this change. You have to active this change by using the following cmdlet:
Set-CsPlatformServiceSettings – EnableExternalAccessCheck $true