I've just read it ! I don't think storing sensible informations on the blockchain is good. You could never delete a message, or even send a "full size" email, with images and so on. Why ? because there's a limitation on the amount of data in each transfer (around 8 kb). Plus, having to spend money to send a message is in my sense pretty archaic. Nobody wants to pay money for sending a few words. In addition, 0.001 steem might be nothing today, but here is a post (in french) from somebody who told in 2010 that 0.1 bitcoin were nothing : https://ploum.net/monnaie-de-geek-monnaie-de-singe/
Anyway, thanks for providing me this, I will definitely try to find a way for Steemians to filter messages if they wish so ! And also, thanks for your support !