What's your go-to lead list building method for cold outreach?

Hi everyone! I have recently started two cold outreach campaigns which are performing pretty well, but the biggest blocker is being able to compile leads quickly enough to generate any kind of scale.

My method so far has been pretty manual: I research relevant businesses that fit my target, then find the right person to contact, and then finally find their email using Apollo. I've also tried creating larger lists through targeted searches in Apollo, but as you can only export 25 at a time this has felt like a really clunky process.

I feel like I must be missing something - how do you scale list building?

I often see people talking about how they send thousands of emails a week and - while that's not my goal right now - I just don't understand how it's possible to generate lead lists that big.

Does anyone have any nuggets of wisdom on how to do this at scale?

Side note - check out this amazing guide written by a fellow indie hacker with so many practical steps for anyone that's relatively new to cold outreach (especially all the technical stuff involved in the set up)