Remove winmail.dat file from Office 365

This is an issue with Hosted Exchange. The fix required logging into the hosted exchange using powershell and running the following:

$LiveCred = Get-Credential

$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell/ -Credential $LiveCred -Authentication Basic -AllowRedirection

Import-PSSession $Session

Set-RemoteDomain Default -TNEFEnabled $false

Remove-PSSession

Remove-PSSession $Session