If your server has problems resolving domains Error "unkown host domain.com" (mostly with OVH servers) , just change the DNS server.
Debian 9 / CentOS
Debian 10 / Ubuntu
sudo nano /etc/resolv.conf
remove the existing Nameservers and replace with this.
After this Save editings with CTRL + O and press enter, then press CTRL + X to close Nano Editor.