I've been running a SaaS in the email space since 2011. It is not surprising at all, to me, that Mailgun decided to do this.
Sending an email _is_ trivial - you're right - but getting it delivered to the inbox, instead of the spam folder, is far from trivial. At scale, it is incredibly difficult. Even worse, spammers and fraudsters are utterly relentless. They hammer services like mine and Mailgun's constantly with fraud and phishing and porn and other garbage, inbound and outbound.
Sending an email _is_ trivial - you're right - but getting it delivered to the inbox, instead of the spam folder, is far from trivial. At scale, it is incredibly difficult. Even worse, spammers and fraudsters are utterly relentless. They hammer services like mine and Mailgun's constantly with fraud and phishing and porn and other garbage, inbound and outbound.