There's a prefer-ip6 option but no corresponding prefer-ip4 option.

Many service providers are unable to consider the reputation of any source address smaller than a /64 but many VPS providers put all customers in the same /64.

This makes it impossible to reliably use IPv6 for outbound connections. For example, sending any email to Google over IPv6 will significantly reduce the likelihood of it being delivered.

When querying DNS blacklists/whitelists that impose a query limit based on source address, the only viable solution at this time is to prefer IPv4 whenever possible.

Ideally I'd like to be able to configure specific zones to be IPv4-only with a require-ip4 option.