Email configuration with auth returns SMTP Error: data not accepted

There was a post some time ago which is about the security option: Kirby->Email / SMTP Error (Timeout?) - #10 by jango Seems like 'security' => true is not correct, but 'security' => 'ssl' or 'security' => 'tls'. Check also if you are using the correct port (which seems to be the case here).