Nonstandard E-mail Attachments of type: "application/ms-tnef", and "winmail.dat" attachments

Gregory Harris, gharris@math.ku.edu
Created: January 2005

Microsoft has decided to invent a new way of sending files attached to E-mail messages. The attachment will be hidden inside of a file attached to the e-mail message called "winmail.dat". This format is called "Transport Neutral Encapsulation Format" or TNEF. Most E-mail readers cannot receive attachments of this type. This includes Mozilla Thunderbird, Apple Mail, and pine. Only very few E-mail programs can read these attachments, which include Microsoft Outlook, and Microsoft Outlook Express, and the Horde/IMP Webmail that our department uses.

If you receive an attachment of this type, I strongly encourage you to send an e-mail back to the sender and ask them to turn off the winmail attachments, since so many people cannot read them. You can send them a link to this page for instructions on how to turn TNEF attachments off. If they are still having problems, it is possible the administrator of their mail server has overridden their settings, and therefore the administrator will need to change them on the server.

For Attachment Senders, How can I turn off sending TNEF attachments?

Note: These instructions are from Microsoft and are for Microsoft Outlook 2000. Other versions may require different procedures. If you are still having problems with the recipient not receiving attachments, please contact your technical support person.

People using Microsoft Outlook can turn off the winmail attachments by the following method:

1. On the Tools menu, click Options, and then click the Mail Format tab.
2. In the Send/Compose in this message format list, click to select Plain Text, and click OK.

This method is documented in the Microsoft Knowledge Base, OL2000: "Attachments Not Visible to Some Recipients When Using TNEF", available at the following link: http://support.microsoft.com/default.aspx?scid=kb;en-us;Q197066

For Attachment Recipients, How can I download the attachments inside of the 'winmail.dat' file?

You can use the Horde/IMP webmail program available at https://www.math.ku.edu/mail. The name of the file will be linked, and will usually be at the bottom:

At the top of the message you will see the usual headers, as well as a "winmail.dat" attachment.

At the bottom of the message you will see the components of the "winmail.dat" attachment. In this case it is the file "Password Policy 10-17-04.doc". If you click on the filename you will be able to download the attachment.

Please note, if you forward messages with TNEF attachments to other users with a mail program that can't understand TNEF attachments, the recipient will not be able to receive the TNEF attachment from your forwarded message.