Mozilla Thunderbird is the email client provided by Mozilla who are famous for their web browser Mozilla Firefox, which brought about a revolution in browsers for the internet. Sometime users may receive a message in rtf format that cannot be viewed by Mozilla Thunderbird. For this, one needs to download specialized software to decode the Winmail.dat file. To view a RTF file there is a downloadable program available which is first used to open the file. After that, the Winmail.dat file should be saved in the same location and needs to be run from the same directory.
It may happen that when you receive a message the attachment is not displayed under Mozilla Thunderbird and you have a winmail.dat file instead. This happens when someone send you an attachment in the format .rtf format, specific to Microsoft, is not supported by Mozilla Thunderbird.
Install the following plugin: LookOut for Thunderbird (free and open source - MPL License).