[bitfolk] IPv6 reverse DNS

I currently relay email for a customer who has a Hetzner server [1].

We had problems sending email as we share an IP address block
with habitual spammers (OSLT - much argument on the mail operator's
mailing list - basically, live next to noisy neighbours, you might
find yourself with an ASBO).

So I relay his mail (obvs., not an *open* relay!).

I used verifier.port25.com and got a fail on the reverse IP
lookup, as they use IPv6.

Bitfolk.com says:

"For IPv6 we can delegate the IPv6 reverse zones to your nameservers. We
can also provide up to three secondary nameservers for you."

and the domain is registered and has DNS provided by 123-reg. Which
doesn't seem to know about IPv6.

Do I have any other options apart from using a different DNS provider?

Or moving the domain away from 123-reg?

[1] Only place I know of where you can get 12TB of disk for "not
too much". We need lots of disk!