You are correct, the mail server is currently configured to only receive emails via IPv4. This setup is not uncommon as most major email providers have IPv4-only MX records (with Gmail and Yandex Mail being rare exceptions that support IPv6).
It might be a good idea to provide a different email address whose mail server explicitly requires IPv6. I'll think about it. Thanks for bringing it up.
It might be a good idea to provide a different email address whose mail server explicitly requires IPv6. I'll think about it. Thanks for bringing it up.