Epitaxial Fe3O4(001)/MgO(001) films obtained by reactive molecular beam epitaxy were studied using a combination of in situ scanning tunneling microscopy (STM) and monolayer Fe-57 probe Conversion Electron Mossbauer Spectroscopy (CEMS). For the as-grown films the (root2 x root2)R45degrees surface reconstruction was observed in agreement with the earlier studies. UHV annealing considerably improves the films' surface quality (the lateral size of the terraces) but it inevitably leads to the diffusion of magnesium into the magnetite film resulting in pronounced changes of the surface structure as seen in LEED and STM. Correlation of the STM and CEMS data indicates a more complicated surface termination than the homogeneous octahedral or tetrahedral one. A charge redistribution in the surface layer evidenced by CEMS can be responsible for the surface reconstruction. Despite the surface structural and electronic modification, the presence of the Verwey transition in the surface layers is proved by low-temperature CEMS.