Not sure what you mean, but communication itself and its effect on human culture does not change, no matter the media. You can draw a painting to de-humanise and incite hatred towards a group, or you can go on radio and incite hatred towards a group. Either way, both methods can be used to incite hatred.
also includes many lessons we’ve learnt since 1930s.
Sorry I forgot to address this.
Correct me if I am wrong but I don’t see how we learnt since. As we speak, a used to be unknown far-right party gained massive electoral votes in Romania. It turns out that they have been making their presence in social media, where older establishment politicians have no familiarity with. The bigger lesson that democratic and liberal forces should do is knowing to use new forms of media instead. Franklin Roosevelt and Barack Obama knew this very well.
I don’t know where you reside, but can’t you write on the back of the envelope containing the letter with “return to sender”? In my country, this is what we do to notify the sender that the addressee no longer lives in the premise.