Has nothing to do with 'vacuum' or 'sucking'.
For every action there's an equal and opposite reaction. So, if you throw a mass in one direction YOU will be pushed in the opposite direction. The more momentum (amount of mass or the additional velocity) that you impart then the greater the opposite reaction.
This is also true if the mass that is being thrown happens to be air. The engine uses the chemical energy in fuel to raise the temperature (adding heat energy) of the air flowing through it then converts that heat enercy into velocity (kinetic energy).
It effectively shoves the air out of the back a lot harder than the air came in. The net result is the engine experiences a reaction in the opposite direction.
Even in space where the vacuum is all around (apart from the immediate vicinity of the efflux) this is the case. If it weren't, all those satellites & astronauts up there are in for a very rude surprise - quite apart from the ones waiting to go.