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Your new Exchange server sends Winmail.dat attachments to recipients on a Mac

This is an old issue, but it still affects modern version of Exchange (yes even Exchange 2013). Basically emails sent from a corporate email server running Microsoft Exchange will appear to have a Winmail.dat attachment when received on a Mac computer using the native OSX mail application. This can happen regardless of the email format settings in Outlook on workstations using the Exchange server to send email. One of the more common suggestions for solving Winmail.dat attachments via Google is to configure Microsoft Outlook to not use the “Rich Text” email format option. While this can also cause the issue, Outlook 2007 and higher has used HTML message format by default and there is actually an Exchange setting that can be responsible. With TNEF Message Formatting set to $true, outgoing exchange emails may be sent in such a way that our friends using OSX get those pesky winmail attachments. Here’s how to set this exchange feature so that doesn’t happen:


  • Microsoft Exchange Server 2010+
  • Windows PowerShell with the Exchange commandlets

[step 1] Launch the Exchange Management Powershell and execute this command:

Set-RemoteDomain Default -TNEFEnabled $false

That’s it.

June 3, 2014

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