In a Microsoft Skype for Business Server 2015 environment, you use a Skype for Business UCWA 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 internalalways 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 January 2019 cumulative update 6.0.9319.537 for Skype for Business Server 2015, Web Components Server and the January 2019 cumulative update 6.0.9319.537 for Skype for Business Server 2015, Front End Server and Edge Server.
After you apply this update,
If the caller uses the Skype for Business on Mac desktop client that connects an external network, the Is From User Internal flag will be marked as No.
If the user of the Skype for Business on Mac desktop client is a callee, or the client is a mobile client, it will keep the original behavior.
In addition, this update currently only addresses the issue for the sender side. For the value of Is To User Internal (receiver side), the issue is fixed in May 2019 cumulative update 6.0.9319.548 (CU9) for Skype for Business Server 2015.