E-Mails are cleared out from IMAP-folders after mailbox migration

[Thomas Hejze]

The background:
I own a private domain and use the service of a provider for E-Mail services 
to that domain. Because my long term provider decided to impose a migration 
from IMAP/SMTP to Microsoft356 upon its customers, I had to change my 
provider. I decided to do that by making a local copy of all my E-Mails in my 
inbox and all IMAP Folders below and then copy them back to an IMAP/SMTP 
account which was set up freshly at my new provider. All this should by done 
by Kontact/KMail.

System: kdepim/akonadi binary packages of a standard OpenSuse 15.6 
installation, version: 23.08.5, release bp156.1.3.

After sucessfully setting up the fresh account I moved E-Mails and folders 
back to the Inbox. Then the first weird thing occurred: Some of those folders 
reappeared in the local folder structure. I removed those obvious duplicates 
by deleting the folders one by one in the tree view.

After a few minutes I noticed that some of the folders in the IMAP tree were 
cleared out (not all!). Fortunately I had a backup on an external harddisk, so 
I was able to restore the missing E-Mails in a local tree (although it took 
quite some time). However, after copying the E-Mails from their local to the 
corresponding IMAP folder the same happened again. The IMAP folders were 
emptied again after a few minutes.

I repeated this several times, always the same. I can confirm that the E-Mails 
were copied to the server of the provider, I checked this via Webmail. So 
there must be something in the client/agent/akonadi chain that makes that 
undemanded folder clearence.  

Please give me some advice, how to solve that problem.

Best regards
Thomas Hejze