We report a comprehensive high-level explicitly correlated ab initio study on the X- + NH2Y [X,Y = F, Cl, Br, I] reactions characterizing the stationary points of the S(N)2 (Y- + NH2X) and proton-transfer (HX + NHY-) pathways as well as the reaction enthalpies of various endothermic additional product channels such as H- + NHXY, XY- + NH2, XY + NH2-, and XHY- + NH. Benchmark structures and harmonic vibrational frequencies are obtained at the CCSD(T)-F12b/aug-cc-pVTZ(-PP) level of theory, followed by CCSD(T)-F12b/aug-cc-pVnZ(-PP) [n = Q and 5] and core correlation energy computations. In the entrance and exit channels we find two equivalent hydrogen-bonded C-1 minima, X- ... HH'NY and X- ... H'HNY connected by a C-s first-order saddle point, X- ... H2NY, as well as a halogen-bonded front-side complex, X- ... YNH2. SN2 reactions can proceed via back-side attack Walden inversion and front-side attack retention pathways characterized by first-order saddle points, submerged [X-NH2-Y](-) and high-energy [H2NXY](-), respectively. Product-like stationary points below the HX + NHY- asymptotes are involved in the proton-transfer processes.