Can outsider emails reach college professors, or are their emails programmed to block emails that are not from within the university?
Also how would a high schooler go about emailing a college professor about research opportunities during the summer?
I emailed many professors for the same thing and I got very few responses. I’m not sure that college professors offer many positions or research opportunities at this time, especially for high school students. Also they could be on vacation 
If you are interested in this summer, then it probably is too late to arrange a position for you. Assuming you are focusing on a local university, perhaps your GC or teachers in your high school will know which local profs have worked with students before. If you are interested in working with a professor who directs a project or lab with multiple staff, then perhaps you could try emailing one of the postdocs just to see if you have better luck. Contact info might be on the professor’s lab’s website.
I agree with @CheddarcheeseMN. It is most likely too late for this summer. However, you could always reach out just to try and see if there is anything possibly during the school year that you could do. You could also just ask them about interning next summer too.