IPv6-only MiaB test server

It would be nice if MiaB or any of its fans would set up a permanent MiaB with a friendly domain and an account or two that is IPv6-only and let us use for testing. The idea being that I could send an email to test_user@ipv6only.mailinabox.email and if it gets there I know IPv6 outbound works on my server. If the email gets back to me from this test server, I can then confirm that IPv6 is working inbound.
I suppose it would make sense to also have testuser@ipv4only.mailinabox.email