I am having this same problem a year later. Anytime i send mass invoice emails through quickbooks "send forms". All my recipients complain the same. They are getting a winmail.dat file. I have already done all the recommended setting changes through outlook. They are already on the setting for HTML or plain text when using the outlook program. This is a quickbooks problem. I am tired of reading how its outlooks problem. When i use the outlook program no one has a problem, but when i use the ''Send Forms" for my invoices of customers this is what happens everytime. I have even changed my preferences for send forms and checked the use "plain text" format for emailed invoices and they still are getting it.