They finally started receiving fan mail... which is interesting since all these episodes went live on Netflix on the same day, so unless the post office can deliver letters backwards in time there is no way they could have recieved the letters before they filmed this episode.

Yes, that was rather unconvincing, wasn't it? Presumably the fanmail came during/after the Kickstarter campaign.

Even in the original series I was always surprised how almost all the letters came from young children. They can't possibly understand the majority of the jokes and yet this is clearly a family show where the kids just like the robots while the parents laugh at the riffing.