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Exchange: Mail attachments are turning to winmail.dat

This is a very common issue but I just wanted to highlight the component which supposed to be changed here.

The issue is when one messaging system user is sending an attachment it is becoming winmail.dat. I recently got this issue in mail flow between IBM Lotus notes Domino to Microsoft Exchange 2010.


Here are the steps to fix it

  1. Login to your exchange server
  2. Open Exchange management Console
  3. Go to Organization Configuration à Hub Transport
  4. Select “Remote Domain” tab
  5. Go to the properties of the Default Domain
  6. Select “Message Format” tab
  7. Now you can see the problem is “Determine by individual user setting”


  8. Change “Exchange rich-text format” to “Never use” like the screen below

  9. Click Apply then ok.
  10. Restart Microsoft Exchange Transport server on every Hub transport server.


This should fix winmail.dat issue.


Prabhat Nigam

Microsoft MVP | Exchange Server


7 Responses to “Exchange: Mail attachments are turning to winmail.dat”

  1. Anexus Says:


    Thanks for this article.
    I have this problem last week in Exchange 2013.
    I cannot found this menu in ECP2013.

    Do you know if there is a power shell command ?


  2. Prabhat Nigam Says:


    2013 has in the shell. Below is the cmd. Dont forget to restart Transport service.

    Get-remoteDomain | set-remoteDomain -TNEFEnabled $False

  3. Anexus Says:

    Many Thanks.
    I’ll try it tomorrow morning.

  4. Blog Posts of the Week (6th - 12th October 2013) - The South Asia MVP Blog - Site Home - TechNet Blogs Says:

    […] Exchange: Mail attachments are turning to winmail.dat […]

  5. Chris Says:

    I already have this option disabled, and some users are still sending mail and it is appearing as winmail.dat, any ideas how this is possible?

  6. Prabhat Nigam Says:

    Check if they are using rich text format in their outlook and the issue is only with outlook.
    you might need to update outlook or exchange server. What is you outlook and exchange level?

  7. Martin Roy Says:

    This worked for me with Exchange 2010 & Outlook 2013.. No more winmail.dat attachments.. Thanks…

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