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Konstantinos Tsoukalas

Konstantinos is the founder and administrator of Since 1995 he works and provides IT support as a computer and network expert to individuals and large companies. He is specialized in solving problems related to Windows or other Microsoft products (Windows Server, Office, Microsoft 365, etc.).


  1. Steve S
    November 4, 2019 @ 8:04 pm

    Hi Constantinos,
    Many, many thanks for your excellent guide on how to cure this Winmail.dat problem. I loaded several updates for MS Office. Suddenly Outlook 2010, which had worked fine up to that point started to convert every attachment to Winmail.dat. I had tried the HTML/Plain text format fix and modified the registry to disable TNEF. Nothing had worked. The thing that made the difference was outlook.exe /cleanautocompletecache. Thanks again – I was about to hit my computer with a big hammer!


  2. niko
    May 27, 2019 @ 2:12 pm

    thank you dear for winmail.dat 2013 outlook solution. Regedit+… fixed the situation


  3. rws70
    April 7, 2019 @ 1:43 am

    Are you F'ing kidding me? The solution to MS Outlook not being to send pasted in picture files all this time such that an iPhone user can see the picture is a simple registry Dword fix?

    This is why there is a love – hate relationship with Microsoft. The winmail.dat issue has been such an annoyance. They could have fixed this long ago, and instead they allow it to continue. The registry fix is the way to go.

    Thank you so much for posting this.


  4. Joe
    March 14, 2019 @ 4:06 am

    Great job, fixed my problem :)


  5. Anneli
    December 20, 2018 @ 12:37 pm

    This problem occurs when you send an email by using recipient format:

    When you use only using format: there is no winmail.dat problem!

    I think Microsoft should fix their software because the issue is so simple.


  6. Alesia Perry
    July 24, 2018 @ 2:14 am

    Thank you so much!!! I can't tell you how long I have been trying to find a solution to the very irritating winmail.dat issue. I had tried solution #1 multiple times, and it never worked, but solution #2 did the trick!! I was on the verge of using a completely different email app even though I wanted to stick with Outlook 2016. I can now continue to use Outlook 2016 because of your help. Thank you!!


  7. Wil
    May 1, 2018 @ 9:46 pm

    Awesome!! Thank you for resolving my pet frustration which MS couldn't …. with reference to

    Your suggestion to delete the Outlook.NK2 file in %APPDATA%\Microsoft\Outlook did the trick just fine


  8. Carl
    June 30, 2017 @ 6:21 pm

    Thanks a lot. The solution to add the DWORD entry in the Registry actually works for Outlook 2003 as well. Just go to 11.0 instead of 12.0


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