he - net - ipv6 - admin ** ! **

confirm delivery of email sent to SMTP server - set up ipv6 enabled MTA - used postfix, added

/etc/postfix/main.cf:
    # You must stop/start Postfix after changing this parameter.
    inet_protocols = ipv4       (DEFAULT: enable IPv4 only)
    inet_protocols = all        (enable IPv4, and IPv6 if supported)
    inet_protocols = ipv4, ipv6 (enable both IPv4 and IPv6)
    inet_protocols = ipv6       (enable IPv6 only)

whew.