I'm having the same issue.
It seems like there's a discreprency between what is removing/expecting the leading zeros in ipv6.
For example, my VPS' ipv6 reverse DNS control panel removes leading 0's.
The mail-in-a-box status page seems to expect the leading 0's to remain.
"This domain should resolve to your box's IP address (AAAA (ipv6 with leading 0's)) if you would like the box to serve webmail or a website on this domain. The domain currently resolves to (ipv6 without leading 0's) in public DNS. It may take several hours for public DNS to update after a change. This problem may result from other issues listed here."
All the default AAAA records using the (ipv6 with leading 0's).