In the previous version of MAlL
In the previous version of Mail you could have a Subfolder named "2019" in several Folders. I sort my mail into the main Folder with the year as a subfolder. I appreciate that you cannot have duplicate Folder name but I cannot see the reason for taking the ability to create the same subfolders names in different Folders. You can, at the moment create a Subfolder with the same name as a Main folder.
eg. Folder A and Folder B could have subfolders 2017,2018. 2019.
This was very very useful. I now have to have Folder A with subfolder 2019 and Folder be has to be 2019a.
Please amend the few current lines of code to be as they were in the previous version which I am sure is an oversight.