A few weeks ago when i was trying to join an online match in the horizon 3 and it was impossible, after doing a bit of research i find that the server connectivity was blocked.
After doing all the steps tha microsoft says and serching i surrendered.
The really problem became when i start horizon 4 ans the error appeared again, the same DNS error.
My solution, formating windows 10 and surprise IT WORKS or at least is still working ( i formatted yesterday)
I hope this fix could help anyone.
Btw my English is a little bit … Rubbish so sorry for the mistakes