How will SMTP servers vet sources of inbound messages within an IPv6
I don't know, but except for very limited corner cases, trying to use a
source address to vet the source in an IPv4 environment is foolish and
error-prone. It is no less foolish and error-prone in IPv6, but that's
not the fault of IPv6.
from my experience
- very few SMTPv4 servers look at PTR/A record matching. i'm not sure
how i can configure sendmail/procmail to do this.
- i never found any RBL-style blacklist for IPv6.
- spammers DO use SMTPv6. by chance or by intention? not sure.
- more and more ISP SMTPv4 servers do filter SMTPv4 from outside of
its network, to prevent the abuse by spammers.
- more and more ISP infrastructure practices OP25B for IPv4.
i'm not too sure about the latter two in IPv6. maybe we should ask
NTT and IIJ email ops division about this.
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