Yes to smart filtering at the right layer. The whole reverse DNS checks et al. are so effective. I recently moved my personal mailbox from a host who didn't do these kinds of checks to one that does. My received spam volume instantly went from about 20 a day (across all my aliases) to less than 1 a week.
replySPF and DKIM are now more commonly implemented correctly by spammers than by major email providers.
replyYes, but they are still effective at preventing spam from spammers who are pretending to be others.
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