Thunderbird saying unknown


I am teaching a student to use Thunderbird with NVDA and when they are reading a message, NVDA will say "unknown" if they hit tab out of the body. It will also say unknown if they hit tab out of the list view of the messages.
This on Windows 8 with the latest version of Thunderbird and the latest version of NVDA.

Thunderbird is really easy to use, but is there an email client that is just bairbones emails and folders?
Thank you,

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