What is this warning message ?
I have mailboxes for ALL ACCOUNT, why I receive this message ?
It's pretty much self-explanatory - if you have configured mailboxes to used the new mdbox format then this script has limited functionality accessing them. If you have not started using mdbox and are still using maildir then it will continue to function as is. If you do not understand the difference between maildir and the new mdbox you need to investigate them yourself.