We describe a new model for studying intermittently connected mobile networks, based on Markovian random temporal graphs, that captures the influence of message size, maximum tolerated delay and link stability on the delivery ratio. Categories and Subject Descriptors C.2.1 [Network Architecture and Design]: Store and Forward Networks; C.4 [Performance of Systems]: Modeling Techniques General Terms Theory, Reliability Keywords Delay Tolerant Networks, Random Temporal Graphs, Message Size, Delivery Ratio