Moving mail to a public folder in Apple Mail deletes the mail
In Apple Mail, if you try to move a message to a public folder for which you only have read-only ("reader") rights. You do not receive an error as would be expected and the operation appears to work correctly. However, the message does not appear in the public folder and is lost.
This is caused by an bug in Apple Mail - it is not caused by Kerio MailServer. In technical terms, Apple Mail doesn't check the response to the IMAPInternet Message Access Protocol - One of the two most commonly used Internet standard protocols for e-mail retrieval, the other being POP3. COPY request because it behaves as it succeeded even when it fails. The problem occurs with all read-only folders. This problem also happens with other mailservers, e.g. MS Exchange.
A bug has been filed with Apple. Until this is fixed in Apple Mail, you should educate your users to avoid this bug.