Iron fluorescence emission is ubiquitous in HMXB systems. The iron fluorescence emission originates from the binary environment populated by the dense stellar wind of the companion stars in the HMXB systems. A large collecting area and excellent sensitivity near the iron fluorescence band make XMM−Newton an ideal instrument for studying the reprocessing environment in these systems. We studied bright HMXBs like GX 301-2, Vela X-1, and Cen X-3, which also have a high iron line equivalent width. We use the pulse-phase resolved variation of the flux from the lines to study the structure of the reprocessing environment in these systems. Spin-phase dependency in the fluorescence emission is not likely to originate from a homogeneous and isotropic binary environment. A pulsed fluorescent emission can originate from the accretion disc, the accretion wake, the companion star's surface, or clumpy stellar winds from the companion star. In the case of GX 301-2, the strong iron Kalpha fluorescence emission was found to vary with not only the spin rotation of the NS but also with an additional periodicity. Using detailed phase-resolved spectral analysis, we investigated the origin of the second periodicity. The most plausible scenario is a clump of wind material in a Kepplerian orbit about five lt-sec from the NS. In the case of Cen X-3, we found a spin-variable component from all the iron K-alpha and K-beta emission lines, which can be formed when the accretion stream in the NS cuts the line of sight of the observer. The excellent spectral resolution of the Resolve instrument onboard the XRISM telescope allows it to measure the relative motion of the emission lines around the binary orbit. The orbital motion of multiple fluorescent lines can be used to put tighter constraints on the possible origin of the reprocessing emission.