If you are not using Microsoft Outlook, you maybe know this problem: You get an email
from somebody using Outlook with an attachment called winmail.dat. If you would use Microsoft
Outlook you would not see the attachment but the real attachment(s).
This problem appears when somebody sends e-mails in RTF (Rich Text Format) with Microsoft
Outlook. If the receiver uses Thunderbird, Mozilla, Netscape, Opera, Eudora etc. to view
emails, he cannot see the contents of the winmail.dat.
How to tell Outlook not to send the winmail.dat
Have a look at the Microsoft Knowledgebase to prevent Outlook from sending
that file: Microsoft Knowledge Base.
How to extract the winmail.dat contents
This small tool KM.winmail enables you now for opening, decoding, viewing, converting and extracting the contents of the winmail.dat file.
This tool is
freeware and licensed under the GPL as it uses the libytnef.
Supported Operating Systems
W9x, NT, 2000, XP.
1) Download the viewer version 1.1
2) Unpack it to a location of your choice, e.g. c:/programs/winmailviewer/
3) When double clicking the winmail.dat attachement in your browser, enter the
location of the unpacked kmwinmail.exe
From now on, the winmailviewer will be opened for your Outlook attachments files.
After double clicking the attachment in your mailer, the viewer opens under
the mouse cursor:
Select the file you are interested in with your left mouse button. Now you can
choose the actions with the buttons:
"Open" opens the file with the registered application.
"Save" saves the choosen file. A save-as dialog comes up.
"Save All" saves all files in the archive. A save-as dialog comes up.
To open the file directly without using the menu just double click the file in
If you have any feedback for me, send me an e-mail to
You can download the source code
- Initial revision. Can open winmail.dat files with attachments.
- Resolved error with paths that are enclosed by apostrophs ("). This
is done automatically by windows when a path with spaces is passed.
- Upgraded to libytnef 1.5.
- Show message if the winmail.dat is a vCard, vCalendar or vTask.
Other tools you could use to view the winmail.dat