Thunderbird definitely is not on the list of currently supported mail applications, which currently are limited to Microsoft Outlook 2010, 2013, and 2016: https://www.virtru.com/faq/which-platforms-are-supported-by-virtru/ Since they have an extension for Firefox, and Thunderbird has many of the same communication capabilities as Firefox, I think the company likely could support Thunderbird as well. I don't know whether they have any interest in doing so. If you are a fan/user of their products, you might contact them to learn more about their plans, if any.