The PowerShell cmdlet associated with the Top senders and recipient report which is Get-MailTrafficSummaryReport(Get-MailTrafficSummaryReport (ExchangePowerShell) | Microsoft Docs) will be retired as well.
You are receiving this message because our reporting indicates one or more users in your organization are using the Top Senders and recipient report. Moving forward we recommend using the Threat protection status report: Threat protection status report
What you need to do to prepare:
Instead of using Top Senders and recipient report, we recommend using the Threat protection status report. You may consider updating your training and documentation as appropriate.