Email List Services (or simply, mailing lists) are becoming increasingly common for collaborative computing. In order to enable their use for official purposes with increased effectiveness and security, services typically provided by postal mail (e.g. fair delivery) need to be provided in mailing lists. In this paper we propose a novel Certified Mailing-list Protocol (CMLP) that provides fair delivery, confidentiality, nonrepudiation of origin and receipt, and authentication and integrity. We have formally specified and verified the CMLP protocol with Proverif, which is a fully-automated protocol verification tool. Categories and Subject Descriptors H.4.3 [Communications Applications]: Electronic Mail Keywords Mailing lists, Certified delivery