virtual shared folder (n)~ A mailbox folder structure on some IMAP servers in which mail folders are accessed with the administrator username and password and shell login access to the mail server is not allowed. Access to specific mailboxes is managed by access control lists. This means that users are assigned the permissions to only access their mailbox folder while an administrator has access to all mailboxes. This allows organizations to use administrative credentials to migrate e-mail from an IMAP server to Outlook Live.