Extmail inbox is full, can't delete mail, can't clear mailbox space

Error message: insert REC206 err;

Method Enter your domain name in the "/home/domains/" directory, find the user name, enter MailDir, delete the extmail-curcache.db file, and log in again to refresh the mailbox. The premise is to increase the mailbox space as much as possible, and then Do the above operations, leaving room for reserved operations.