I agree that email is an attention-sucking mess, but I see the problem differently from jacobjacob. I would happily get all the emails from the rationality community; my problem is that email is dominated by marketing, mailing lists, etc.
I think that using earn.com is likely to exacerbate the problem of unrequested marketing emails. It is free to send messages, and the sender only pays upon receipt of a response. This is like selling advertising on a per-click-though basis rather than on a per-view basis, and if it took off I would expect spam to quickly dominate the platform. Even if the message model were modified to incur costs for sending a message, I still think that many companies would gladly pay to send messages over a trusted high-status channel (similar to how fundraisers include stickers or cash in their mailings to raise the likelihood of you reading the materials). I'm not sure that friends and contacts would value my responses enough to match corporate calculations.
One reason to escew earn.com specifically is the use of bitcoin. Proof-of-work cryptocurrencies are a major waste of energy (0.2% of the global energy use currently) and should be avoided by rationalists.