Let's say a plane EM wave passes through an air molecule. To explain scattering classically, you can consider an electron held to the rest of the molecule by a spring that makes a forced oscillation at the frequency of the wave. You can show that if the frequency of the wave is way smaller than the natural frequency of the electron (which is the case for visible light on air molecules), then the oscillating electron will emit an EM wave in phase with the incident wave, at the same frequency, in almost every direction, having an electric field whose amplitude depends on the direction and is proportional to the square of the frequency. This implies that blue light is scattered more than red light, which explains why the sky is blue. This is fine.
The explanation that sunsets are red because if blue scatters more, then a white beam of light from the sun has lost more blue and thus apppears red makes sense. However, it doesn't tell me what the mechanism responsible for reducing the E-field of the blue wave is! In my mind, the only way the E-field can decrease is by destructive interference, but the E-field produced by the molecule is in phase and it interferes constructively with the incident E-field! Even if you allow for damping (to take care of radiation resistance), you get a scattered E-field that is 90° out of phase with the incident E-field, which doesn't reduce the net E-field.