AI has been participating in that war on both sides. All the big providers use some form of AI to identify spam [1]. And on the other side several startups (some advertised here!) are offering AI-driven mass mail marketing (They use AI to customize mails and to identify targets) [2].
1. https://workspace.google.com/blog/identity-and-security/an-o... "Gmail employs a number of AI-driven filters that determine what gets marked as spam."