Now with IPv4 I'm using the re-mailer of my ISP as it doesn't allow me to go out on port 25 to other host (via IPv4). So postfix forward all the outgoing email to the ISP.. I'm wondering if I can avoid this behavior with IPv6, if there is any SMTP public provider that accept mail delivery via IPv6 and if I can configure Postfix to direct-deliver the mail if a server is IPv6-capable and use the re-mailer if it is not (maybe with a server ipv6 whitelist).
I'm not sure if http://ipv6.rollernet.us/ is what you're looking for or not