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This report is for Exchange Online users. This is because Office 365 does not return tracking information about messages sent by delegates " on behalf of " another mailbox - or "delegator" - and therefore it is impossible to show who sent messages " on behalf of " another Exchange recipient in the traffic reports. The workaround used is to count the Outlook items sent by delegates in the delegator's mailbox.
You will first need to enable copying of items sent by delegates into the delegator's Sent Items folder using the following PowerShell command:
Set-Mailbox <delegate's email address> -MessageCopyForSendOnBehalfEnabled $true
Count messages sent by delegates " on behalf of" another mailbox in the Sent Items folder of the delegator's mailbox.
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