[Dovecot] whole user mailbox read only

Hello, i was browsing the dovecot wiki for some documentation related to the use of ACLs but i couldn't find an answer.

i'm in the need to prevent users from deleting emails, yet being able to add new content via imap, what i mean is that a user should be able to create an email in its mailbox (maildir actually is used), but once the email is there the user shouldn't be able to delete it.

do you know if there is a way to accomplish this for each subfolder on a Maildir environment?

Thanks in advance Francesco