Name servers. Most registrars provide two or more name servers as part of the registration service. However, a registrant may specify its own authoritative name servers to host a domain's resource records. The registrar's policies govern the number of servers and the type of server information required. Some providers require a hostname and the corresponding IP address or just the hostname, which must be resolvable either in the new domain, or exist elsewhere. Based on traditional requirements (RFC 1034), typically a minimum of two servers is required.
GoDaddy hasn't traditionally had an uptime policy for its older CPanel email. But since the company has transitioned to Microsoft Office 365 for its email services, it's now able to enjoy Microsoft's 99.9% uptime guarantee. However, be aware that GoDaddy has replaced the Office 365 health services dashboard with its own internally branded version. It shows the same kinds of information including when the last issue was, and whether or not it's been resolved.