Part of the ESX-3 specialized secretion system, which is required for siderophore-mediated iron acquisition and for the secretion of EsxH and EsxG. Part of the ESX-3 / type VII secretion system (T7SS), which is composed of cytosolic and membrane components. The ESX-3 membrane complex is composed of EccB3, EccC3, EccD3 and EccE3. Deletion of the gene impairs iron-bound mycobactin utilization and EsxG and EsxH export. Belongs to the EccD/Snm4 family.