Thanks for quick response!
One more missunderstanding i have: as far as i understand this option u mentioned will allow to login into e-mail accounts using both - LDAP and internal authozitation methods at the same time, right? If i migrate authorization to external LDAP to users, than how i gonna be able to link that
user1@mydomain.com authorized internally right now is the same
user1@mydomain.com with same IMAP box, but right now authorized to external LDAP?!
Sorry, if it is too stupid question

, but i didn't find this information in none of the topics and i really need to be sure about all the topics i'm interested in before i start to migrate.