I tried to make kmail create some mbox files in order to archive some e-mails in a portable and readable way. However, I cannot get the name of the resource to be displayed properly, and it doesn't work immediately without applying an extra step which should be unnecessary.

STEPS TO REPRODUCE

1. In the "configure kmail"->"Accounts"->"Receiving"->"Add...Custom account" dialog, I choose "Mbox". A dialog window opens and, before I fill any field, an account named "akonadi_mbox_resource_[some number]" appears in the list of accounts in the "configure/accounts/receiving" window, but not in the list of folders in the main window.
 
2. In the filename field of the configuration dialog, I enter "foobar.mbox" and click "Ok". the name "akonadi_mbox_resource_[some number]" appears in the folder list of the main window. It is still present under that name in the "configure/accounts/receiving" window. No file "foobar.mbox" is created.

3. In the "configure/accounts/receiving" window, I select the "akonadi_mbox_resource_[some number]" account and click "Restart". Three things happen at the same time:
    *) a notification message appears, reading "The resource 
       akonadi_mbox_resource_[some number] is not working. No file specified."
    *) in the "configure/accounts/receiving", the account   
       "akonadi_mbox_resource_[some number]" is renamed "foobar.mbox"
    *) the empty file "foobar.mbox" is created 

However, in the folder list of the main window, the resource is still named "akonadi_mbox_resource_[some number]", and I can find no way to change its name to foobar.mbox or anything else. The resource seems however to be working: I can move messages to it, and the appear in the foobar.mbox file.

So, I guess I have three related issues; from most important to less:

*) In the folder list of the main window, the proper name "foobar.mbox",
   or whatever I choose in the configuration dialog, should be used, rather
   than "akonadi_mbox_resource_[some number]".

*) When creating the Mbox account, I should not be required to 
   "restart the resource"  before it starts working.

*) As a user, I should never see an internal name such as 
   "akonadi_mbox_resource_[some number]", even temporarily.
   In particular, nothing should appear in the 
   "configure/accounts/receiving" window before I enter a filename.

This is on an uptodate fedora 32, with kmail-19.12.2-1.fc32.x86_64, plasma-workspace-5.18.5-2.fc32.x86_64, kf5-akonadi-server-19.12.2-2.fc32.x86_64, qt5-qtbase-5.14.2-8.fc33.x86_64.