But ebay does ask for verifying addresses with postcards. Banks ask for verification of addresses. [...] I don't think that post-its in the apartment building's door are an efficient way to communicate. If I could reach all the people in my apartment digitally, I do think that would be great. The problem is rather that it's unlikely that other people in my apartment building would sign up for such a service. When I pack up packets for neighbors I sometimes would appreciate a digital way to contact the neighbor. To effectively implement it in Berlin I think there are three choices: 1) Go to big landlords like degewo. Sell them on the idea that it's an added benefit to have communities in their apartments. Then let them communicate information that's currently communicated via hang-outs via the website. 2) Cooperate with government programs for neighborhood building in the Soziale Stadt category. 3) Focus on vibrant areas in Friedrichshain and Kreuzberg with a lot of young people who are eager to adopt new technology. Encourage new people who sign up to do hangouts in their houses. From those 1) is likely the best strategy. It shouldn't cost degewo much money. Having a digital channel to their rentees might even save them money. Degewo runs ads so they care about having the image about being different from other landlords.