I have several Co-domains installed on a single ISP site sd-1494.dedibox.fr Their DNS configuration is identical. However, one Co-domain has a DNS problem. Users outside the hosting ISP periodically cannot access the domain without typing "www." as a prefix, some domain.net does not work, whereas www.domain.net does work! Under ISP Manager > vihinfo.net > Co-Domain > Domains: 188.8.131.52 papamamanbebe.net 184.108.40.206 www papamamanbebe.net 220.127.116.11 lemegalodon.net 18.104.22.168 www lemegalodon.net 22.214.171.124 survivreausida.net 126.96.36.199 www survivreausida.net Under DNS Manger > DNS Entry > Records for papamamanbee.net (example): A Record 188.8.131.52 Hostname www 184.108.40.206 Hostname mail MX mail.papamamanbebe.net Hostname: www sd-1494.dedibox.fr Hostname: mail When I try to make changes (like remove the Hostname www from MX record mail.papamamanbebe.net) I get the following error message: This or a similar MX Record does already exist in this zone. My questions: - When I create a Co-Domain under ISP Site, should I also add Hostname www in addition to the domain on its own? - When I add a New Master under DNS Manager, what is the correct configuration for a Co-Domain?