I'm using Roundcube mail on Windows 10 with a localhost Wamp. Below are some comands that I found in an answer to the same issue of storage-server-failed but I don't know where to execute these commands or use GUI to remove the devcot files on my Windows 10 PC.
cd /home
/etc/init.d/dovecot stop
rm -f */imap/*/*/Maildir/dovecot*
rm -f */imap/*/*/Maildir/.*/dovecot*
rm -f */Maildir/dovecot*
rm -f */Maildir/.*/dovecot*
/etc/init.d/dovecot restart
It was solved by starting Mercury Mail in Xampp. And creating user in Mercury Mail.