Winmail.dat is attached to email instead of a .pdf file when sent from QuickBooks through Outlook
Recipients of files sent through QuickBooks receive an attachment called Winmail.dat instead of a .pdf file. This is a known issue for Microsoft outlook if the recipient's email client is not capable of receiving rich text format (.rtf).
If only one or some customers experience this issue, it can be due to a problem on the receiving end. Certain security and mail filters may detect these emails as mass emailing (spam) and must be adjusted accordingly.