[lol_catz]

SMTP will never go IPv6 in my opinion.

IP reputation scoring is feasible with 4.3 billion IPv4 addresses.

That model breaks down when you’re dealing with 340,282,366,920,938,463,463,374,607,431,768,211,456 possible IPv6 addresses.

[scatbot]

That's not how SMTP reputation scoring works. Even in IPv4 per-IP reputation stopped being sufficient many years ago because bulk senders churn pools and rotate addresses. Modern systems typically score prefixes, ASNs, DKIM/SPF alignment, TLS and behavior.

[benjojo12]

About 58% of all of the email my company sends out of it's outbound relays is to IPv6 MXs. I've never really had to deal with discoverability issues related to v6

[patmorgan23]

Microsoft and Google both have IPv6 addresses published for their MX

[winstonwinston]

I published AAAA records for my MX hostnames a few years ago and so far only gmail.com is sending mails via IPv6, which is disappointing.

[mono442]

You can score subnets instead of individual ips.

[RupertSalt]

Perhaps you mean “prefixes” such as they are assigned by registrars, and announced by routing protocols.

The instructor of my Cisco classes said that the only module that caused students to break down in tears was VLSM.

[db48x]

Weird. Once I made the analogy with street addresses that are divided into blocks then subnet masking was pretty easy to understand.