Micro- to mesoporous iron(III) trimesate MIL-100(Fe) is a MOF of high interest for numerous applications. With regard to large-scale synthesis, e.g., by continuous flow or the in situ deposition of coatings, a replacement for the conventional, hydrothermal low-yield fluoride-containing synthesis is desirable. In this contribution, we present a method to synthesize crystalline fluoride-free MIL-100(Fe) from iron(III) nitrate and trimesic acid in zeotropic DMSO/water solution at normal ambient pressure involving a DMSO–nitrate redox pathway. Yields of 72%, surface areas of S_BET = 1791 m² g⁻¹ and pore volumes of V_pore = 0.82 cm³ g⁻¹ were achieved.