It is forbidden to smoke in the building of Sheremetyevo International Airport and within 15 meters of entrances to the terminals.
By the end of 2018, Sheremetyevo plans to construct seven roofed pavilions for smoking near the passenger terminals. The pavilions are designed for 12–14 people, and are equipped with ventilation systems and are isolated from the rest of the Airport premises.
Research indicates there may be some places you can smoke inside the terminal (a number of lounges) however this is prohibited and you do so at your own risk.