Comment 2 for bug 247396

Thank you for reporting this bug and helping make Ubuntu better.

Do you have the 'tnef-attachment' plugin enabled (Edit/Plugins)?

If you do not see it, then you need to install the evolution-plugins-experimental' package. You can do it, for example, by opening a terminal and:

sudo apt-get update
sudo apt-get install evolution-plugins-experimental

After installing the package, close & restart Evolution, then go back into Edit/Plugins, and make sure tnef-attachment is enabled. You then should be able to decipher the infamous winmail.dat.