If @mastodon is 'decentralized like email,' then let's talk about how centralized email actually is: (1) Domain registrars control naming from step one. (2) Spamhaus & similar entities dictate legitimacy, marginalizing entire domains at will. (3) servers must comply with endlessly growing, centralized verification systems just to avoid blacklisting. (4) major providers block small email servers before they even reach Spam.
#Decentralized in name, centralized in effect.