Go to
GMail , open an email you want to block, click or tap More, click or tap "Filter messages like these", set up anything that needs to be set up (I just use the "From address), click or tap "Create filter with this search", check the Delete box, if there's a number greater than 0 in "Also apply filter to X matching conversations." and let it go. Then the emails matching the criteria on the first page will get deleted before you see them, or soon after, depending on the email app you're using. That's about the best you can do, as far as I know.