A count in the millions is not a good sign, it means your filters are describing a market rather than a segment. Narrow in a deliberate order, one filter at a time, and read the count after each change so you can see what each one costs you.
- Add a role or seniority. This is almost always the biggest and most useful cut, because it moves you from every employee to the people who can actually buy.
- Add a company size range. Narrow to the bands where one message stays true. See size bands.
- Tighten geography. Go from a region to specific countries, and only then to states.
- Add a keyword. Use this to carve your niche out of a broad industry rather than adding more industries.
- Exclude titles that keep showing up in the preview and are never your buyer.
After each step, scroll the preview rather than just reading the number. A count that halves while the preview still shows the wrong people means you cut the wrong dimension.
Resist the temptation to fix a large count by exporting a small random slice of it. A slice of a bad list is still a bad list, it just costs less. Narrowing properly gives you a segment you can write specific copy for, and specific copy is what actually moves reply rates.