Yes, you can mix different DNS service providers. However, consider that you need to have the same records and configuration synced between them. Otherwise, you might get unexpected results as different visitors resolve to different DNS configurations.
Unless you know exactly what you are doing, we advise against it. You don’t gain more redundancy as most DNS services that are correctly set up, including ours, have different clusters in geographically separated regions in the world. This is why you enter more than one nameserver in the domain configuration, and the reason domain names require a minimum of two servers. If one nameserver fails, a computer system will try the next working one. This is not in order as most people assume and can be completely random.
Therefore, if you mix different nameservers, you will not get the effect that you probably expect. If you use one provider as nameservers 1 and 2 and a second provider as nameservers 3 and 4, it does not mean that your domain will use the first one and only the second provider when the first failed. It will use all of them and in a completely random order. Technically it’s a bit more complicated than this, and the way DNS lookups are executed are different between different computers or operating systems. Since you have no control over your visitor’s computer’s, you need to assume that all your DNS nameservers will be used.
Most operating systems work by distributing the queries between different nameservers. In this case, if you have different DNS records on provider one and no records with provider two, your domain will continuously fail to load for some visitors while it might work other times.
Often people that mix nameservers in a domain do it by mistake and then wonder why their website points sometimes to one server and other times to another place or does not work. As general advice, unless you know how DNS systems work on the Internet with domain names, you should stick to using a single DNS service provider.
If you currently have no DNS service provider, we offer a service for free with every single domain registered and managed with us. You are free to create and edit your DNS records on your account by configuring your domain to use the default nameservers.