1. A method for sharing referenced content through collaborative business: applications, the method comprising: detecting referenced content in an electronic communication, the referenced content referencing content stored in an external repository, the referenced content identifying a registered external repository connector; determining that an Access Control List (“ACL”) for the referenced content lacks an entry for a recipient of the electronic communication; and generating an ACL entry for the recipient in response to the recipient lacking an entry in the ACL for the referenced content, the ACL entry controlling access to the referenced content for the recipient, the ACL entry defined based on a security policy associated with the recipient.