Magnetic topological insulators such as MnBi2Te4 and MnSb2Te4 are promising hosts of novel physical phenomena such as the quantum anomalous Hall effect and intrinsic axion insulator state, both potentially important for the implementation in topological spintronics and error-free quantum computing. In the bulk, the materials are antiferromagnetic, but appropriate stacking with nonmagnetic layers or excess Mn in the crystal lattice can induce a net ferromagnetic alignment. Accurate control of the materials growth is thus essential to optimize the magnetic properties. In this work, we report a detailed investigation of the growth of (Sb2Te3)1–x(MnSb2Te4)x layers with varying Mn content by molecular beam epitaxy. The Mn flux fraction provided during growth controls the percent of MnSb2Te4 that is formed in the resulting layers by a self-assembly process. Highly crystalline layers with compositions varying between Sb2Te3 (x = 0) and MnSb2Te4 (x = 1) were obtained. The results show that Mn is incorporated as a structural component to form septuple layers (SLs) of MnSb2Te4. Excess Mn was observed in the samples, suggesting that it is incorporated as antisite defects into both Sb2Te3 and MnSb2Te4. Two modifications of the growth conditions were implemented to enhance the incorporation of Mn as a structural element to form MnSb2Te4 SLs: annealing of a thin portion of the layer at the beginning of growth (preannealing step) and increasing the growth temperature. Both result in a larger percent of MnSb2Te4 SLs for similar Mn flux fractions during growth, increasing the control of the growth and providing insight into the Mn incorporation process.