The low-lying ionization energies and fine structure splittings of highly correlated systems, Zn and zinc-like ions, are computed using relativistic multireference many-body perturbation theory with large Gaussian-spinor basis sets. The relativistic multireference perturbation calculations reproduces the ionization energies of Zn and zinc-like ions to unprecedented accuracy, with the largest deviation between theory and experiment of 0.17 percent. Contributions to the ionization energy of relativity, Dirac-Coulomb and Breit correlation corrections, and the Lamb shift, are analyzed.