> IPs -- You need to send from a variety of IPs. They have warmup time before they can be safely used. One bad guy can burn that IP and everyone who shares. Most ESPs aren't going to have dedicated IPs for each (or those are for high tiers).

I'm curious, is that specific to IPv4 or you see the same phenomenon with IPv6 where providers allocate /64 or /48 to customers? Or there simply isn't enough sending volume from IPv6 at the moment to warrant specific filtering?