Recently had a client who uses QuickBooks to email invoices to their clients via Outlook.
In some cases, when emailing the invoice to a client the client receives a Winmail.dat file, rather than their invoice in PDF format. Usually, Windows displays a warning message via a Desktop Windows Notification.
In my experience, the main reason why this occurs is because of a corrupt contact entry or autocomplete entry inserted into the “TO” field by QuickBooks (or Outlook).
Simply removing the TO field recipient email address (prior to emailing the invoice) then manually reinserting the email seems to resolve this. In my experience, future emailed invoices to this particular client will work without issue because the corrupt contact entry has been updated (when you manually reinserted it).
If deleting the autocomplete entry does not resolve your issue, try deleting the actual Contact entry in Outlook (if one exists).
I welcome your thoughts, questions or suggestions on my article on resolving the issue of QuickBooks invoices leaving Outlook as winmail.dat instead of PDF.
Let me know if you found any errors within my article or if I may further assist you by answering any additional questions you may have.