The main tenets of the theory of spatial diffusion of innovations are considered. The analysis revealed a key problem, namely one of seeking to reduce to two kinds the whole variety of techniques for diffusion of innovations. The searching for the third kind of diffusion is exemplified by innovations related to the expansion of Siberia’s postal network. Seven such innovations were identified. Five of them were diffusing across space in the form of postal-innovation waves. The simulation model for one wave is presented. It is concluded that there exists a network diffusion of innovations.Keywords: diffusion of innovations, postal network, postal-innovation wave, simulation model, network diffusion, Siberia.