Re: Questions concerning Thunderbird
1. I can't see that (Sent Date or anything similar) in the list of things you can display in Thunderbird. If you want to have a look yourself then see: http://accessibilitycentral.net/accessible%20email%20client%20mozilla%20thunderbird.html and look for the section entitled, "Using drag and drop with NVDA to rearrange column headers in Mozilla Thunderbird." Even if you don't plan to rearrange anything it lets you get into what's available to rearrange and that's not necessarily visible by default.
2. Do you have more than one e-mail account set up in Thunderbird? I have not seen the 4-notifications with 4 different message counts but it strikes me as if it could be a mailbox by mailbox feature, as in version 52 there is a single system tray icon where you get the counts for individual mailboxes on hover-over. I don't see anything obvious in Tools, Options that would make this happen but it's the only rational explanation unless something's not working right (which, of course, could be the case).
Brian Version 1703, Build 15063.296, Home 64-bit
Many are under the gross misapprehension that the Constitution is a cage and a laundry-list rather than a framework upon which great things have been and still will be built. Many things that are entirely Constitutional are not "in the Constitution," but are allowed under it.