Last reviewed on July 28, 2015   —  97 Comments

Applies to Microsoft Outlook 2013, Outlook 2010, Outlook 2007, Outlook 2003 and older

There is a long standing “problem” between Outlook and Internet email – Outlook uses a proprietary email format that only Outlook and Exchange (and a few other clients, including gmail) can decipher. When the recipient doesn’t use Outlook, they get a plain text message and an attachment named winmail.dat. Additionally, the attachment icon may be hidden by some clients, including OE and Windows Mail, making it look like the attachment was removed.

The problem? Any attachments included in the message are encased in the winmail.dat attachment.

RTF settings | Email properties of a Contact | Email properties in To field
Turn off RTF Capability | Tools | More Information

Note that if you are using Exchange Server, the Exchange administrators can disable RTF on messages sent to the Internet. SharePoint Contacts linked to Outlook are also a problem. See Other causes of unexpected formatting for more information.

If you arrived on this page because you received a winmail.dat attachment and don’t use Outlook, see the Tools below for utilities you can use to retrieve attachments from the winmail.dat file. Don’t bother looking in winmail.dat files if you were not expecting an attachment (or if the message size indicates there probably is not an attachment).

Or ask the Outlook user to resend the file, using plain text format. If there is an attachment in the winmail.dat, asking for a resend is my preference, in most cases. This way the sender fixes the problem for future attachments. If you aren’t expecting an attachment and the file size is too small for an attachment, you don’t need to ask for a resend, you are only missing the pretty formatting.

What is RTF, TNEF and winmail.dat?

Outlook can use a special method, technically referred to as Transport Neutral Encapsulation Format (TNEF), to package information for sending messages. The use of TNEF is affected by settings in Outlook that are referred to as Rich Text Format (RTF). TNEF and RTF are not identical, but they are very similar.

A TNEF-encoded message contains a plain text version of the message and a binary attachment that “packages” various other parts of the original message. In most cases, the binary attachment is named Winmail.dat, and it includes the following information (if included in the message):

  • The formatted text version of the message (ie, font and colors).
  • OLE objects (such as embedded pictures and embedded Office documents).
  • Special Outlook features (i.e., custom forms, voting buttons, and meeting requests).
  • Regular file attachments that were attached to the original message.

Where to check for RTF settings in Outlook

When RTF is not working as expected (either all messages are RTF, or Meeting Requests and Voting are not working) there are several settings your need to check in Outlook.

Note: Exchange server administrators can also control RTF to Internet addresses. If the administrator disables RTF to Internet addresses, the settings in Outlook will not override them.

Don’t forget to clear the auto-complete cache after changing Outlook’s settings. The auto-complete cache (nickname cache) remembers the setting and Outlook will continue to send messages using RTF. Delete the address from the cache to clear it or clear the entire auto-complete cache. See How to clear name from the cache at Understanding Outlook’s Auto-Complete Cache if you need help clearing the autocomplete cache.

Global properties:

Use this setting to control how messages created using RTF formatting or that require TNEF encoding are handled. If this is set to plain text or HTML formatting, Voting and Meeting Requests may not work unless you override the setting using Email properties.

Outlook 2007 and older: Go to Tools, Options, Email Format, Internet Options button.

Outlook 2007 global settings

Outlook 2010 and Outlook 2013: File, Options, Mail and scroll to the bottom of the dialog.

Outlook 2010 global properties

Recommended setting: Convert to HTML. Outlook will send all messages to the Internet using HTML unless you change the email properties (below).

Email properties of a Contact

Open the Contact and double click on the email address. Changes made here apply to all messages sent to this person. Use this to override the setting in Internet options (above).
Let Outlook Choose

Recommended setting for most contacts: Let Outlook decide. This will send all messages using the global properties. If you need to send Meeting Requests or other messages that require TNEF encoding and know the contact uses Outlook, you can set the contact to always use RTF.

Email properties of an address in the To field of a new message:

Double click on the address in the To field. If the address is in your Contacts folder, their contact opens; if the address is not in your Contacts, the email properties dialog opens. Use this setting to “one-off” the formatting when sending meeting requests or RTF formatted messages to Internet addresses. This will override the setting in Options dialog’s Internet options.

Let Outlook choose

Recommended setting: Let Outlook decide – this will send all messages using the global properties. If you need to send Meeting Requests or other TNEF encoded messages and know the contact uses Outlook, you can set the address to always use RTF.

To access the Email properties in Outlook 2010 or 2013:

In Outlook 2010 you’ll access the email properties from the contact card that comes up when you hover over or click on an address in a Contact or an email message. Select the menu icon on the right and then Outlook properties to open the Email Properties dialog. As with the older versions, the recommended setting is Let Outlook decide unless you need to force RTF.



Reminder: The autocomplete cache (nickname cache) may remember the RTF setting and Outlook will continue to send messages using RTF, overriding the Contact settings. Delete the address from the cache to clear it. (Select the address using the arrow keys and press Del)

Other causes of unexpected RTF formatting

SharePoint Contact libraries synced with Outlook are marked to always use RTF. This is fixed in Outlook 2010 SP1 or the Exchange administrator can configure Remote Domain transports for the domains that don’t use Outlook and set them to never use RTF to get around the problem.


To change the settings on Exchange server, open the Exchange Management Console, expand Organizational Configuration, Hub Transport, Remote Domains, open default transport (or the transport you want to change, if you have more than one) and change the Rich Text setting.

See Configuring TNEF settings on Exchange Server for the PowerShell cmdlets to use and instructions for configuring it in Office 365 Exchange.

Antivirus scanning corrupts the TNEF attachment and the recipients Outlook can’t decode it. This is more common with client side scanners, such as AVG. To fix, disable email scanning on the client side; there is no need to scan email with a virus scanner on the desktop computer.

As mentioned previously, the nickname cache can contain the ‘always use RTF’ flag – if the sender ever forces RTF for one message to the contact, the cache remembers the setting for that contact and always uses RTF (forcing it on the address overrides the conversion setting in Mail format>Internet), even though the contact is no longer set to always use RTF. Delete the address from the cache to fix.


If all else fails…

If nothing seems to be working and you use Outlook 2007 SP2 or Outlook 2010 or 2013, you can use a registry value to end TNEF encoding once and for all. This will affect your ability to use features that require TNEF encoding, including Voting and Meeting Requests in native Outlook format. (Ready-to-use .reg files are available below.)

  1. Close Outlook
  2. Start Registry Editor (type regedit in the Start Search box or Start menu, Run command and press Enter)
  3. Locate the following registry key:

    In Outlook 2007:

    In Outlook 2010:

    In Outlook 2013:

  4. Add a new DWORD named DisableTNEF.
  5. Double click on DisableTNEF and in the Value data box, type 1
  6. Close the Registry editor and Restart Outlook

More information on this registry fix: When you use Outlook 2007 to send an e-mail message, the recipient of the message sees an attachment that is called Winmail.dat

Hotfix for pre-Outlook 2007 SP2 to enable the registry fix: Description of the Outlook 2007 hotfix package (Outlook.msp): October 28, 2008

Hotfix for Outlook 2007: Description of the Outlook 2007 hotfix package (Outlook-x-none.msp): December 11, 2012 – When DisableTNEF is used, read receipts are corrupted and cannot be delivered. You cannot send any email messages in Outlook 2007 and you receive this error message in the Outlook Send/Receive Progress dialog box: Task ‘account name – Sending’ reported error (0x800CCC13): ‘Cannot connect to the network. Verify your network connection or modem.’

Do It For Me

If you don’t want to make the changes to the registry yourself, you can download a .reg file with the changes. Double click to install.

Outlook 2007 Outlook 2010 Outlook 2013

Before using the registry fix with Outlook 2007, you will need to install the Hotfix for pre-Outlook 2007 SP2

Remember to restart Outlook or reboot if the registry key does not appear to work!

To reverse the changes, delete the key from the registry or edit the .reg file in Notepad and change the following line, then save and run it.

“DisableTNEF”=dword:00000001 to “DisableTNEF”=-

In addition to setting the registry kjey (which didn’t appear to have an effect), tristof cleared the cache file:

(I went) one step further by clearing the whole auto-complete cache of Outlook. Outlook > File -> Options -> Mail -> Send Messages section. Click the “Empty Auto-Complete Lists” which will clear the entire cache and it finally worked.

Tools to Recover Attachments from Winmail.dat


Utility to decode attachments sent by Outlook that arrive as Winmail.dat files because you sent in Rich Text Format.

TNEF's Enough

Tool for Macintosh computers to decode the Winmail.dat attachment sent in Rich Text Format messages.

Winmail Opener

Winmail Opener is a small and simple utility that allows users to view and extract contents of TNEF-encoded messages (winmail.dat). Version 1.4 - Free.

Winmail.dat Reader

Open, convert and save the files on winmail.dat email attachments sent by Microsoft Outlook and Exchange. Easy-to-use graphic interface (no command-line tool). Displays the original message subject and body. Free.


  1. Alan K Simpson says

    This is an excellent article. However I still have a few queries.

    It is still a mystery why only some of the email addresses in my contacts file came to be set to "always use RTF". There seems to be no pattern. Any suggestions?

    Is there a quick way of checking the email format setting for 1000 plus contacts and changing it to "Let Outlook decide" where necessary? i.e. is there a default setting for the email address format which will apply to all contacts.?

    How do I make sure that no new addresses creep into the file with the "always use RTF" setting attached?

    I have inserted the registry value to end TNEF encoding, which will presumably do this, as I am unlikely to need the voting and meeting requests facilities in native Outlook. Is this the only solution.

    • Diane Poremsky says

      See - there is a link to a VBA sample that changes the setting on many contacts at once.

      AS for how that came to be set - it's impossible to know. It's possible an older version did it, an import, sync... almost anything. Sharepoint contacts always use RTF - that is fixed in Outlook 2007 /2010 if you have all updates installed.

      No default oprion - it should default to let outlook decide. The only way they'd creep in is if you imported or synced - but normally, sync doesn't cause it.

  2. דפי צביעה says

    I did it all, and yet- when sending emails from our outlook users - allways send as winmail.dat.

    I use exchange 2010 / outlook 2007+2010

    Please help?

    • Diane Poremsky says

      What version of Outlook and what type of email account do you have configured it in? Did you restart Outlook or reboot the computer after setting the registry value?


    i have MS OUTLOOK SP3 and when send a pdf to Blackberry from PC, it arrive convert in winmail.dat

    please, help


    • Diane Poremsky says

      You are sending it on a message that is using RTF format. If the message is HTML, when you type the address in the To field and it comes up, select it using the arrow keys and press delete then re-type it or select it from the contacts.

  4. Antonio says

    Mine is a very strange behavior...User send meeting requests from Outlook 2010. If she sends it directly to someone outside the organization using the exhange server (2010), whom uses the IPhone, this person gets the winmail.dat error and cannot open the attachment. This external individual is also setup on the exchange server as a contact. If the user send it to the contact and exchange forwards the meeting request to the external e-mail, the IPhone user gets it with no problem. If the user sends it using a POP3 account, not the exchange, the external users gets it just fine on the IPhone.

    I checked all the settings on Outlook as well as on the Exchange server and they are all as suggested. The only change I've made is on the Exchange to never use RTF.

    • Diane Poremsky says

      The iphone user is getting winmail.dat even with Exchange configured not to use it to the internet? It may be picking up on the external address on the contact.

      Have the user type the iphone user's address in the To field and delete it when it comes up. If there is a contact for the iphone user, check the properties to make sure its not set for always use rtf.

  5. David S says

    I am have a similar issue... I had my client send a meeting request to two external clients. One is my home email and one is another client who is not getting the meeting notices but just emails with the subject of the meeting notice. I get the meeting request just fine on my home address and accept it. The second clietn still does not. The only difference I see in my external SMTP (Ironport) logs is my home address does NOT have the winmail.dat but the second clients does.

    Any ideas?

    • Diane Poremsky says

      what version of Outlook do you use? When sending to internet addresses, the Option to send icals to the internet is usually better. In Options, Calendar options is an option to use icalendar for internet addresses.

  6. KY says

    does this method work on Outlook 2003? I've already chosen HTML as mail format and added "DisableTNEF" into my registry HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Preferences
    but somebody still received my emails in winmail.dat.
    what else can i do?

    • Diane Poremsky says

      No, sorry. The DisableTNEF key is available in post-Outlook 2007 SP2 and later.

      If only one person is getting a winmail.dat, make sure their contact is not set to always receive RTF and delete their entry from the autocomplete list. (Begin typing their name in the To field, when it comes up select it using the arrow key then press Del key.)

  7. Ciaran says


    Maybe you could help with this issue?

    I send a .pdf attachment to 2 Mac users.

    1 mac user receives a winmail.dat attachment
    The other does not

    This would tell me it is a problem with the receiver, not the sender.

    Would you not agree?



    • Diane Poremsky says

      No,it tells me the one users address is set to use rtf or the autocomplete cache has the address marked for rtf. Check the contact properties and delete the address when it comes up as you type it in.

    • Diane Poremsky says

      They should not be set to use RTF. You should only use RTF to other people on your Exchange server.

  8. Ciaran says

    Hi Diane,

    I understand the relation to RTF, my question is, and confusion;

    If both contacts, who use MacMail to receive emails, are sent the same email from Outlook in RTF, then how is it possible that one receives it and can open the attachment and the other gets winmail.dat?

    And to add to the confusion, I have been sending these contacts emails in RTF (which was default) for over 6 months without a problem, and only in last day or so one person starts experiencing the winmail.dat issue!

    I cannot seem to make sense of that.

    Hope you can shed more light


    • Diane Poremsky says

      I'm surprised it worked fine before, but Outlook can be so weird at times, that it's hard to say what happened. (If you use Exchange the admin can set it to convert RTF to HTML.)

      Did you delete the address from the Autocomplete cache? It could be corrupt for that one person.

  9. Håkon Finne says

    Thanks for excellent assistance in preventing Outlook from *sending* messages in rtf/tnef format with atatchments embedded in winmail.dat files. Is it possible that some *receiving* e-mail servers (Exchange or otherwise) can change an incoming html or plain text message with an attached file (from an Exchange server) into a message with a winmail.dat attachment that contains the original attached file, before it is delivered in the recipient's inbox?

    • Diane Poremsky says

      While anything is possible (although highly unlikely) with Exchange servers, it is impossible with other servers.

      I'd say 99% of the time, Outlook is properly blamed for it, with the Autocomplete Cache a frequent cause. Send things like meeting requests and Voting messages, where RTF is needed , and autocomplete decides the address should use RTF all the time.

  10. Gwenn says

    Hello Diane,
    I am running Outlook 2010 with Window 7 and I am trying to follow your above instructions by changing the setting on an individual contact - However - I don't get the same screens you do! When I double-click on the email address, I do not get the email properties dialog box that you show above with the "internet format" Instead, it simply opens another contact card. What am I doing wrong here? I tried deleting the contact and just re-entering the email address but I still don' see the Properties dialog box
    Please help!

    • Diane Poremsky says

      If you double click on the address in the second contact, do you get the email properties dialog?

  11. Sam says

    Hi Diane, I am creating a software that parses winmail.dat files. I found a lot of software on the Internet that are able to do this, but they only do it if it's TNEF encoded. Unfortunately not ALL winmail.dat files are created using TNEF, so in this case I get the error "This is not a TNEF file".

    My question is - Do you know of any software (Free or Proprietary) which can open ALL winmail.dat files irrespective of the TNEF encoding? Please let me know.


    • Diane Poremsky says

      No, if the 4 listed here can't do it, I don't have any other suggestions. If you happen to find something else, please let me know so i can add it to the list.

  12. Jeannie says

    Thank you SO MUCH for this article with the fantastic instructions for both Office 2010 and 2007. The key to fixing this for us was having the additional instructions to clear the Auto-Complete cache. Worked like a charm after we did that. Yay!!!!

  13. Tardif says

    I got Office 2013 on Window 8 and when i send a vCard to an apple user (or an iPhone) it just keep sending winmail.dat

    Extremely annoying, please help !

    • Diane Poremsky says

      Start typing the apple user's name in the To field and delete it from the autocomplete list when it comes up. Type it in again. Does it work correctly now?

      If not, and if the person's contact is set to never use TNEF/Rich text, you can disable TNEF completely.

  14. Tardif says

    Thank Diane for the quick answer. Before sending my question, i did ''disable TNEF completely'' and even then it doesn't work ?!

    Another problem i have with my outlook is that it won't let me open the .doc and .xls files directly from outlook. I need to same them on my desktop and than it's possible ?!


  15. Tardif says

    Yes i did restart outlook. it only create the winmail.dat with vcard (so far)...

    Thank for the Excels problem, It did work :)

  16. Jon Wilbur Ong Tan says

    I most probably will have to deal with the registry. However I'm not pleased with the loss in functionality it will entail.

  17. Lacy says


    Many of the recipents of my e-mails are recieving winmail.dat attachements. Daily I send out mass mailings to customers using Microsoft Dynamics CRM and Outlook and changing the settings for each contact will be difficult. How do I figure out the issue and correct it for all contacts at once?

    Thank you

    • Diane Poremsky says

      What version of Outlook do you use?

      It's possible that the problem is with dynamics integration - SharePoint had that problem too and changing the setting to not use RTF lasted until the next sync. We regularly sent mail to the same domains so the Exchange admin configured the server to never use RTF to mail sent to the domains that had problems with RTF formatting.

      If that is not possible, I'd use the reg key under the If all else fails section. If you need RTF for some messages and can do all the dynamics work in a block, you can set the key then remove it so RTF works again. Use one registry key to set it, one to remove it. (Restart outlook after changing the key).

  18. ron says

    I think Microsoft have become psychotic. Microsoft software is so confusing to use it is just a pain in the ass to get anything done. Simple trivial things that I could do with live mail now elude me. For instance, I cannot attach a word document to an email and send it: I do not know how to forward an email anymore. I get error messages that are incomprehensible such as adding a profile to mail. I am just exhausted. It was even confusing to find out how to print an email, I tried the print feature under File but it does not work, finally I found another print command under three dots on the tool bar that actually prints the email. Under three dots ***. Wow: what is going on?

    • Diane Poremsky says

      Forward is under reply. :) See FAQ for some answers, new question and answers will be at Outlook Tips.

      Can you not find the Insert button or does it fail to insert files? There is a bug with adding attachments and some people can't.

    • Diane Poremsky says

      The reg key will work - Edit registry to block winmail.dat. I need to check on a cmdlet for hosted Exchange. I know there is a problem with office 2013 and 365/hosted exchange as I'm always sending winmail.dat to a yahoo mailing list and I tried all the usual suspects and it keeps coming back.

  19. Tim WIza says

    i checked the registry and the reg key was already there and I am still getting the winmail.dat issue. any other areas I should be checking? Any Help will be appreciated

    • Diane Poremsky says

      Did you restart outlook after the key was added? You're using it with Outlook 2013? I'll retest it, I last tested it during the beta.

    • Diane Poremsky says

      I'll check it - i need to check it in 2013 too. It's possible an update broke it.

  20. Bart says

    We are using Outlook 2010 with Outlook 365 and all solutions are still producing the WINMAIL.DAT file. Any results on your testing???

    • Diane Poremsky says

      This is Office 365 hosted Exchange? In my case, it seems to work only if autocomplete is disabled. Which makes no sense if the problem is office 365.

      Have you (or the exchange admin) tried disabling it at the server? remotedomain cmdlet does the magic.

    • Diane Poremsky says

      I finally got rid of the %$&# thing by creating a remote domain - the only problem i can see is that it did not work to change it for the default, it only worked when i set up a remote domain for a specific domain, which is not practical for hundreds of domains.

  21. Lee Peacock says

    Diane - wow - thanks! this fixed my invite problems! is there a way to make sure each contact is set to the "let outlook choose the best format" option besides going into each email address and checking the properties?

  22. Leena Kanerva says

    Brilliant! I have suffered of this for years: some receivers complain that they receive winmail.dat from me. Some iPad users. But not all. I have not been able to identify the pattern, even I have tried.
    The solutions I have tried: don’t use rtf when sending. I don’t, I use always html, but that doesn´t help. Use plain text of course helps, but it is so ugly.
    The funniest thing is that I have a colleague that has got his current Outlook from same source as I - it is Outlook 2013 from MSonline. He does not send winmail.dat to the same receivers I do. The possible explanation is, that my Outlook 2013 setup has carried the TNEF settings from my earlier Outlook versions (where at some point they have got crooked).
    The regedit addition HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Preferences DisableTNEF=1 fixed this finally for me!
    Million thanks!

    • Diane Poremsky says

      TNEF settings are stored in the autocomplete cache so it is highly likely that Outlook 2013 carried TNEF information over from your previous install. Glad to hear you got it fixed!

  23. DT says

    Hi, I am having the same issue, outlook 2013. Added the registry value, but still the same. The Mac Outlook recipient is receiving winmail.dat. The only thing I can add, is that the sender client is using MS Dynamic CRM...

    Any idea?


    • Diane Poremsky says

      If Outlook is sending the message, the registry key to disable all RTF should work. Did you restart Outlook?

    • Diane Poremsky says

      does the recipient receive winmail.dat files if you use other messages with attachments, or are only the CRM messages affected?

  24. DT says

    Hi Diane,
    the recipient receives winmail.dat even if the message is untracked, sent via plain text and with no attachment at all.


  25. Steve says

    I did the Global properties & Email properties of a Contact. That corrected the Winmail.dat problem. Everything works perfect again. I can see all attachments on my cell phone again.

  26. Jess says

    I am using outlook 2003 and send HTML emails, that do not have attachments, to an apple user who only just recently started to receive them mis-formatted and also with the Winmail.dat attachment. I tried sending plain text, but then the message body loses its formatting.

    • Diane Poremsky says

      Remove the persons email address from the autocomplete list. Does that fix it? If not, verify their contact is not set to always use RTF.

  27. Jess says

    Removing the contact from the autocomplete list might cause a problem for anyone covering my desk.
    I was able to put the intended message into a word document and provide it as an attachment and the recipient stated it worked for them.
    I sure wish outlook and apple could just get along =/

    Thank you for your help and quick reply.

  28. ronaldone says

    I can't figure out how to set the Internet format for a contact in OL 2013. It looks different from 2010 and I just can't find it.

  29. markgrogers says

    Hello Diane,

    Thanks for all the information. It seems that if helps a lot of people- unfortunately, I am not one of them so far.

    The Disable TNEF regedit did not work for me.

    I wanted to try changing the Internet format for a contact- I am using Outlook 2013. Like "ronaldone" above, I cannot get the control you show in the Outlook 2010 screen shot above to appear.

    So I tried to do a regedit for the LegacyGAL key, but I didn't have an "Office" entry under "Policies". Fortunately, your downloadable reg key worked and added it to the Registry for me.

    I re-started Outlook 2013, but still no love... I watched the video you kindly provided, but I do not get any dialog that shows an Internet Options selection for a contact- no amount of hovering, double-clicking or selecting things brings that dialog up.

    Is there something else I can try to get the legacy dialog to appear?

    Thanks again,


  30. ronaldone says

    Still can't find that dialogue in OL 2013 – even after having set the TurnOnLegacyGALDialog key. I am using Office 365 University (which shows as Office 365 Home Premium) at home and Enterprise (which shows as Office Professional Plus 2013) at work.

    I find it kind of unintuitive and laborious to get to that "Internet format" dialogue in OL 2010 but at least I am still always finding it there. I am getting really curious if it actually exists and where it hides in OL 2013!

    • Diane Poremsky says

      They broke it in Outlook 2013 but I'm not sure when - the last time I checked it in 2013, you could get it using the legacygal key. I have a note into support about it.

      ETA: the TurnOffHoverFunctionality key makes it easier to access as the Hovercard doesn't come up until you click and it's what removes the command from the menu.

    • Diane Poremsky says

      BTW, if you are really, really quick in right clicking after you open the contact, Outlook Properties might be on the context menu, especially right after reopening outlook. Once the properties command is gone, you need to restart outlook to get it back.
      This video shows how to do it.

  31. nzeltzer says

    I'm surprised that Apple hasn't incorporate winmail.dat support into something like Preview; sure, it's not "their problem", but then again neither is our need to view PDF files, Excel documents, etc.

    That said, there are literally dozens of apps available to open winmail.dat files. I'm partial to LawBox's Winmail DAT Viewer on the Mac on iOS, but, as I said, there are literally dozens of options.

    Go with the one you trust.

  32. Ger van de Kolk says

    Hello Diane,

    Exchange 2010. Where to clear the RTF in the Exchange administrator tool?
    Thanks in advance


    • Diane Poremsky says

      In the Exchange management console, it's under Organizational Configuration, Hub Transport. double click on the Remote domain then click Message Format. (It's the last screenshot in the article.)

  33. Lindsay says

    I changed the Registry, deleted the cache of contacts, and changed the "Send to internet users" to convert to HTML only and still no luck when it comes to MAC and iPhone users.

    Using Outlook 2013.
    What happens is that i'm preparing several emails with statements in QuickBooks and then Outlook sends them.
    It seems to only happen when a batch of emails are being sent and it would be ridiculous to have to send each statement individually.

    Is there anyway to completely prevent Outlook from converting the files to Winmail.dat?

    • Diane Poremsky says

      If the registry entry in 'if all else fails', no I don't know how to stop it. What type of email account are you using?

  34. Ravi says

    Diane, I would like to make the registry edit change for a user who is using Outlook 2003.

    Is the following key correct?


    Do I create the same DWORD named DisableTNEF? =1?

    I did try this but it is still sending winmail.dat files.

    The issue is slightly different for this scenario. We have Microsoft Dynamics NAV 2009 with the EasyPDF add-on. The user is a warehouse employee and he generates Purchase Order Confirmations that he emails out to our Vendors in PDF format. His Outlook is setup for Plain Text only. Somehow the process of creating an email with a PDF attachment from Dynamics NAV must be changing the email to Rich Text in the background.

    We have checked the email before sending it, to confirm it is Plain Text and not HTML or Rich Text, but it is still received with a Winmail.dat file. There are no email addresses in his outlook or cache as all of the email addresses are in NAV and are pushed to the email .

    The only solution I can see, would be to disable the TNEF function but I am unsure of the path or if the DWORD is the same, or if this is still an option for Outlook 2003.

    • Diane Poremsky says

      That key is only available in Outlook 2007 and up. If upgrading is not possible, can you run a macro? It might work to convert the message to plain text on send (it depends on when Outlook sets it to RTF.)

  35. Allister Bradley says

    Thank you SO MUCH for posting this. I have read through too many posts which suggest my WINMAIL.DAT problem would disappear if I simply changed my mail format to HTML, but that did nothing for me. Your registry edit finally saved me!

  36. paolo says

    Thanks for this thorough article. really useful to help work towards a solution for me. For ME - I rdeleted my fancy signature, and wrote a simple one. This solved the problem.

    Obviously im my case the (broken) html signature was breaking the email + word documents formatting causing a .dat to be sent instead.. Hope someone finds this useful!

  37. JS says

    Hello! I have tried to use RTF and the registry, but it just couldnt work. not using any fancy signature as well. using outlook 2013 to send to yahoo mail. please help!

    • Diane PoremskyDiane Poremsky says

      Did you use the registry file or edit the registry yourself? Did you restart Outlook?

      Are you using Exchange server?

  38. Len Raphael says

    Until last week, the only recipients with the win dat receiving problem of pdf attachments were AOL recipients. I changed the global settings of Exchange 365 to send plain text to AOL recipients.

    But last Thursday I started getting the problem with gmail recipients.

    • Diane PoremskyDiane Poremsky says

      The default Exchange online setting is to never send winmail.dat or TNEF to internet addresses. if you are allowing TNEF to the internet, you'll need to change the setting for gmail addresses too.

      Normally, gmail deciphers winmail.dat files - I wonder if they stopped doing that. (I'll check.)

  39. johnnyzone says

    I've had this problem with one single contact for months now. I tried every solution on here, but none of them fixed the problem for me. Finally, I figured it out. First, I started typing the person's email into the To box, then highlighted it and hit Delete. Then I removed the contact from my Contacts completely and re-added him. After doing this, I can once again send attachments and even pasted images to him! I got this idea from your post, Diane, so thank you!

    • Diane PoremskyDiane Poremsky says

      Thanks for the update - I have a client who is having problems and the reg key to disable TNEF is not working. I'll suggest this to her.

    • tristof says

      In addition to the registry trick (which did not solve the problem at first), I followed johnnyzone's advice and went even one step further by clearing the whole auto-complete cache of Outlook
      Outlook > File -> Options -> Mail -> Send Messages section
      Click the "Empty Auto-Complete Lists" which will clear the entire cache
      and it finally worked. I've had this problem for 8 months, so I'm glad it's finally solved ;-) Thanks Diane and johnnyzone!

    • johnnyzone says

      @tristof, awesome, glad to help! It was quite the relief to finally get Outlook working again, so I'm glad it worked for someone else.

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