Deleted message items are still being gathered and listed in Mailbox Content and Mailbox Attachments Reports.
The Exchange Mailbox Content and Attachments gathering task will gather messages from ALL Folders in the mailboxes, including the Deleted Items. Hence, the messages would have to be deleted permanently to avoid MessageStats from gathering them.
If a message was sent to User A and B, to permanently delete this message, the message needs to be deleted from Sent Items.However, it is to be noted that this will only move the message to Deleted Items. The message will have to be deleted again from Deleted Items container.
There will be a prompt indicating "Are you sure that you want to permanently delete the selected item(s)?", Select Yes to delete it.
If Mailbox A or B will be gathered by MessageStats, they must permanently delete the message. Otherwise, this message will still be discovered by MessageStats. The same applies for received messages stored in Inbox or user-created folders.
In addition, MessageStats may still gather this message because of the Exchange Retention Policy:
If the retention policy is configured to keep deleted items for 8 days, then the deleted messages will appear in MessageStats report for a period of 8 days. After the set period has lapsed, the message will be removed permanently and no longer listed.
An Enhancement Request has been created for this to be considered for inclusion in a future product release:
TFS #192166 - Option to ignore/exclude items in the the Exchange Dumpster for gathering task.
The following steps have been suggested as a workaround:
Ensure the messages have been permanently deleted from the Deleted Items and the Exchange Dumpster.