We keep getting e-mail attachments in winmail.dat files and can't open them. What's going on? Is there a utility that can extract the attachments from these?

When Outlook or Outlook Express users send e-mail composed using Rich Text Format, the attachments often get transmitted in winmail.dat form, which contains the material in ms-tnef format.

Many other mail clients cannot unpack these. Often, Outlook Express can't open them either. The Microsoft Knowledge Base answer is to have the sender re-send the e-mail in plain text format.

There are tools that can retrieve your documents from the winmail.dat file. A Web-based extractor  lets you upload the winmail.dat attachment and have the extracted file returned. You also can download the software the service uses under the general public license.

A desktop utility called tnefclean is available. Another utility, WMParser, is free.. For Linux systems, the Debian version can be installed with the command "apt-get install tnef." A Web search on tnef or winmail.dat will provide other extraction tools.