You can add this functionality by installing the thunderbird-contracts package. Unfortunately it's only available in the elementary OS daily PPA.
It's not recommended to add the daily PPA to your sources, since it contains unstable versions of several system components and may break your system!
Download the desired package and install it manually:
I have Thunderbird 60.2.1 working on Juno and I am using the date formats exactly as you request (I'm in the UK and am very definitely of the English English camp...). In System Settings > Language & Region I have "United Kingdom" as Region, "United Kingdom" as Formats. I have also clicked on the "Set System Language" button (requires unlocking the ...
A workaround I found was using AppEditor (from the eOS AppCenter) to create an application icon for Thunderbird. This makes it function like it would normally, including working native notifications.
Credit to blureshadow on reddit!
It's weird. Thunderbird is showing for me in AppCenter. But if you want to install it manually, open a terminal and type the following commands. You will have to type your password when requested:
sudo apt install -y software-properties-common
sudo add-apt-repository ppa:mozillateam/thunderbird-stable
sudo apt-get update
sudo apt-get install thunderbird
Note: The follwing instructions valid when you loginto your mail via thunderbird. Also this is the normal(default) behavior for thunderbird (also for geary). See note 2.
Enable the "Messaging Menu ...." and restart.
If you got any message, the panel icon shows blue dot, like:
AFAIK, thunderbird does not have a ...