Catalyzes the hydrolysis of sphingomyelin. Sphingomyelinases D are produced by some spider in their venoms, but also by arthropods such as ticks, or pathogenic bacteria and fungi. They might play a role in pathogenicity through different mechanisms, such as membrane destabilization and host cell penetration, but also pulmonary inflammation and cutaneous lesions. a sphingomyelin + H2O = an N-acylsphing-4-enine 1-phosphate + choline + H(+) Binds 1 Mg(2+) ion per subunit. Sphingomyelinase activity is reduced by 33 percent following addition of EDTA. The SMD-tail motif is highly conserved and may be responsible for structural stabilization. Belongs to the sphingomyelinase D/phospholipase D family.