My folks use Tbird to access their email. Recently had an issue where
email could not be received, but could be sent. They did not change
any settings in tbird, then after a few days it started working
normally again.

Problem is that they seem to have lost all their old email, folders,
etc, and the only stuff in their inbox is email & folders that they've
received & setup after the whole issue.

Any suggestions on any possibilities of recovering their saved email,
or is it all lost?