MC250533 – Microsoft will retire the Forwarding report from Microsoft Defender for Office 365 beginning June 14, 2021.
You are receiving this message because Microsofts reporting indicates your organization may be using the Forwarding report.
What you need to do to prepare
Instead of using the Forwarding report, Microsoft recommends you use the Auto forwarded report (https://admin.exchange.microsoft.com/#/reports/autoforwardedmessages), which is where they will continue to invest their resources.
You might want update your training and documentation as appropriate.