The B2C ISPs have moved to domain-based reputation filters that key primarily on authenticated domains and use user interaction to determine if an email should go to the inbox or someplace else. Content filters are largely no longer about simple keywords so much as identifying deceptive and abusive mail. ISPs watch for evidence that a sender sends to users that requested and want their emails.
Gmail has a non-traditional feedback loop that sends anonymized campaign-level complaint data. Gmail Postmaster Tools is accessible to anyone who can prove ownership of a domain or subdomain via a DNS update. This data follows the authentication domains (primarily DKIM) as well as the "From:" domains. Gmail may separate subdomain reputations if the subdomains clearly have separate content. Microsoft uses SNDS to show IP reputation information and uses rate-limiting soft bounces to indicate domain reputation issues. Microsoft intends to move toward a more domain-focused reputation filter in the near future. Yahoo and AOL are all on Yahoo's filter and mail server infrastructure, but still maintain separate feedback loops. Watch for Oath to change this in the future as things are consolidated and rebuilt internally.