Hi,

For people using 365 and send a lot of email to Mac people. Mac users can received email with attachment winmail.dat but they can’t open it.

This behavior occur when user within Outlook send email in a RTF format.

To force a conversion from RTF to HTML, connect to Office 365 with PowerShell (check on my blog for the login information).

Then run the following
Set-RemoteDomain Default -TNEFEnabled $false

The command will convert the RTF to HTML to all domains.