SMTP ain't dead, it just smells funny.
There is a simple way to make spam a thing of the past. It only requires two things;
The quality of DNS-based and other blacklists varies a lot!
DUL-lists for instance, are supposed to list dynamic IP addresses, but often list static IP addresses as being dynamic. So it's best not to use DUL-lists.
Some lists publish entire /24's instead of individual IP addresses. Don't use these blacklists either (it is OK to list entire IPv6 /64's though).
Some lists delist automatically. Others require manual delisting. The latter will result in more false positives.
Comparison of DNS blacklists
Al Iverson's DNSBL Resource
IP Address Blacklist Check
Fighting non email spam.
These may include snail mail spam, sneaker spam (sales / market droids calling at your door), phone spam (telemarketing) and horizon spam (over the top billboards).