Hi and thank you for your help Francis ;)

I had already tested the IP resolver with Google DNS, but I just realized that the firewall of the company blocked the DNS traffic !!! Also, my server has a DNS entry (/etc/resolv.conf) so I do not understand why I had to add this tag in nginx.

Anyway, with this 2 lines, everything is OK now :

resolver 172.16.42.60; (Our DNS)
proxy_set_header X-Forwarded-Host $host;

Again thank you for your help and for the work you do on this board.

Ps: sorry for my bad english ;)