Love the refund idea — that's a pattern I've been thinking about. "Pay to send, refund if I reply" turns the inbox into a signal market.
Right now the sender pays and gets whitelisted permanently. ...
I'd probably set at $1 on my work email, and $0.10 at my private email. That's because I get lots of cold emails at work, mostly completely useless, but not so many useless emails on my private inbox.
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