Disable TNEF on Office 365 (PDF attachments arrive as winmail.dat)
If you are using Office 365 and are experiancing issues with mail attachment arriving to end users as winmail.dat files you will need to disabe TNEF on your Office 365 tenent.
Connect to Office 365 with power shell commands (see previous post) and run the following commands
Set-RemoteDomain Default -TNEFEnabled $false
To confirm that the setting change was applied use: