Reset email account disk usage stats in cPanel
Sometimes email account disk usage stats are cached for too long. Here are commands, that help fix it:
/scripts/remove_dovecot_index_files --user cpaneluser
/scripts/generate_maildirsize ---verbose -confirm --allaccounts cpaneluser
mv -v /home/$cpaneluser/.cpanel/email_accounts.json{,.$(date +%s)}
Remember to use correct cPanel username.
Reference: https://support.cpanel.net/hc/en-us/articles/1500007877701-cPanel-user-mail-quota-is-large-even-though-there-is-no-email-in-that-mailbox