In a system comprising an electronic smoking device and a capsule (6), the electronic smoking device includes a housing, an electric power source, an electrically heatable atomizer adapted to atomize a liquid supplied from the capsule (6), an interface adapted to mount the capsule (6) at the electronic smoking device, and control electronics. The capsule (6) comprises a shell (30) having a longitudinal axis and containing a liquid. A first end side (32) of the shell (30) is sealed by a puncturable membrane. The capsule (6) is adapted to be mounted at the electronic smoking device via the interface. The shell (30) has a triangular-like cross-sectional shape (50) transversely to its longitudinal axis, in an area which extends over at least part of the shell (30) in a direction along its longitudinal axis.