rescann / reindex / rebuild a subfolder structure

Hi,

an user is missing all mail from a folder and all subfolders which are still saved in the users maildir directory on the dovecot server.

From an imap client she sees the main folder but empty. No subfolders.

She told me with an other imap client and a new created account she has the same problem.

Question: Can I resync / regenerate some folder... index.... something....-files from the dovecot side?

 Thanks for hints and regards . Götz