We consider self-adjoint operators of black-box type which are exponentially close to
the free Laplacian near infinity, and prove an exponential bound for the resolvent in a
strip away from resonances. Here the resonances are defined as poles of the
meromorphic continuation of the resolvent between appropriate exponentially
weighted spaces. We then use a local version of the maximum principle to prove that
any cluster of real quasimodes generates at least as many resonances, with
multiplicity, rapidly converging to the quasimodes.