The PO contact might have accidentally clicked the email that generates a receipt when selecting "I have received all the items." These receipt creation request emails are sent to order contacts for POs lacking a receipt when the invoice is already created.

The email looks like this:

Note: The "Created by" field on the receipt will display the PO contact's name, and the PO audit history will indicate that the system user marked the PO as delivered.

If you wish to disable these system-generated emails in case of a missing receipt, navigate to Configurations > Company Settings > Email Notifications and disable the following setting: