Can't connect to Yahoo from Apple Mail

I can't connect to mail servers of yahoo or gmx anymore out of Apple's mail app on my MacBook Air. Everything worked fine until 3 days ago when I could not send mails anymore, using the Yahoo account and stopped receiving mails from that account too. Yahoo mails work fine in the browser, so user name and password are correct. I followed the advice in an article in Apple help and tried removing the accounts and then set them up new, but I can't even complete the set-up, because Mail won't connect to the mail providers. The same problem exists when I try to set up accounts in Outlook. I have tried to use my iPhone's hotspot to connect, because I though maybe something is wrong with the router, but the problem remains the same. Any ideas?