>If you get a recruiter email for a company that is not that company, it's _always_ junk

Not true. Companies hire recruiters to find employees. Not all companies (especially startups) have their own internal recruiting department.

The flip side is true, though: as a company trying to hire people, every recruiter email that says "I have a perfect candidate for you" is junk. They just invent those people or send resumes of people who aren't even on the job market.