That's exactly how we designed it — tiered pricing per address. Your work inbox gets hammered by cold outreach, so makes sense there. Personal inbox, lower volume, so /bin/bash.10 is enough to filter noise without friction for friends-of-friends.
We already support custom sat amounts per user. You could set niko-work@tanstaafl.email at 10,000 sats and niko-personal@tanstaafl.email at 1,000. The refund idea is interesting too — we're thinking about a 'vouch' system where paying once whitelists you permanently, so it's really just a one-time trust signal.
Want to try it? Send anything to niko@tanstaafl.email — you'll see the gate in action.