Noticed an error in the documentation here:
Mailbox format conversion scripts - Documentation - cPanel Documentation
Seems like the option is not -delete_old_format but -delete-old-format (dash instead of underscores). Wasn't sure where else to report this.
Mailbox format conversion scripts - Documentation - cPanel Documentation
Seems like the option is not -delete_old_format but -delete-old-format (dash instead of underscores). Wasn't sure where else to report this.