I am administering an environment of exchange 2003 where multiple companies have their mailboxes hosted on our exchange server 2003 with frontend and backend technology. Recently, I have encountered an issue where some users of different companies (using IMAP services either through Iphone, outlook or outlook express) are able to look at other companies' public folders. I have heard that exchange server 2003 has a vulnerability where if your mailbox is in A folder/company but you may still see the public folders of companies from A to Z. Please check if there is a way / fix available for any such issue.