Can you add the feature for uniforms to be recognised? This could then prompt Alexa to say you have post if person visited the door with a Royal Mail logo on their clothing. Instead of just motion detected at the front door. I am sure this could apply to other scenarios.
This could perhaps be customised so that this only works at certain times in certain scenarios to avoid criminals wearing uniforms.
I know in the US you have mailboxes more commonly and you have separate device for that but in the UK for the most part we have letter boxes