University of Luxembourg Ucom.ch Modern email and instant messaging applications offer private communications between users. As IM and Email network designs become more similar, both share common concerns about security and privacy of the information exchanged. However, the solutions available to mitigate these threats and to comply with the requirements may differ. The two communication methods are, in fact, built on differing assumptions and technologies. Assuming a scenario of untrusted servers, we analyze threats against message delivery and storage, the requirements that these systems need, and the solutions that exist in order to help implement secure and private messaging. From the discussed technological challenges and requirements, we aim to derive an open standard for private messaging.