Ok, I understand. I had a look at Thunderbird but could not find a way to hide the folders. The only thing I can think about at the moment is that your folder has been hidden on the left. Move your mouse
To show how to generate a certificate request in Exchange 2013. We show this process by using the Exchange Admin Center.
Log into Exchange Admin Center.: First we need to log into the Exchange Admin Center.
Navigate to the Servers >> Certificates…
This video shows how to quickly and easily add an email signature for all users on Exchange 2016. The resulting signature is applied on a server level by Exchange Online.
The email signature template has been downloaded from: