Inbox mails lost - second location?

Hi,

some days ago I could not start KMail because akonadi failed to start.
Rebooting the system did not bring any change, so I made a backup of the
folder ~.local/share/local-mail and renamed .local/share/akonadi to .../
akonadi.bak.
Then akonadi and kmail started again. All the folders and probably all  the
mails in them were restored, but I am missing a lot of mails (from 2015 and
before ) in my inbox (Posteingang) folder. Is there a second location or a
database where mails are stored?
I am using KMail 5.12.3, mails are stored in maildir format. Some years ago I
migrated from thunderbird to KMail.

Thanks for an idea
Reinhard