It’s not complicated until your reputation drops for a multitude of reasons, many not even directly your fault.
Neighboring bad acting IPs, too many automated emails sent out while you were resting, compromised account, or pretty much any number of things means everyone on your domain is hosed. And email is critical.
For context for other readers: this is referring to NAT64. NAT64 maps the entire IPv4 address space to an IPv6 subnet (typically 64:ff9b). The router (which has an IPv4 address) drops the IPv6 prefix and does a normal IPv4 NAT from there. After that, you forward back the response over v6.
This lets IPv6 hosts reach the IPv4 internet, and let you run v6 only internally (unlike dual stack which requires all hosts having v6 and v4).