@NiklasR I wasn't one of the people who voted to close it, but I can see a reason why they may have done so. The issue cannot be with your server, since your server works well from all other networks you've tried. By the same token, it cannot be with your DNS configuration. That leaves your friend's home network as the possible culprit - and ServerFault is explicitly not for home environments. That, I would guess, is why the question was closed with that as a close reason.