Ziftwo doesn't charge you a subscription — it charges the people sending you cold email.
Sign in with Google and connect Gmail. Ziftwo is free for you — there's no subscription.
A message from someone you don't already know gets held. They're asked to buy a stamp — $2.50 each, sold in packs of 8 ($20) — before it's delivered.
Each stamp buys 14 days of access to your inbox, so a sender who's paid doesn't have to pay again for every follow-up.