We have 1 customer that receives their invoice as a winmail.dat instead of a .pdf.  This ONLY happens when we send out bulk invoices in the monthly batch.  If there is a single invoice or an estimate sent to this client, they receive it correctly as a .pdf file.  The sender and recipient are both using Microsoft Office 2019.  This has been a problem for us with both QuickBooks Enterprise Solutions: Professional Services 21.0 and 22.0.  I have set Outlook to send all mail from our side as plain text per QB's instructions.  Creating a non-professional email just to send out bulk invoices to all of our clients is a non-starter, not just from a professionalization standpoint, but also from a security standpoint.  Is there a different mail setting within QuickBooks for sending invoices in bulk compared to sending just a single invoice?