If you are courious what I do with the API access...
Long story short: Nothing. I will not read your mails, send mails, read notifications or calendar events or anything else using https://spacemail.xyz/.
A little more precise:
Everyone registering for an application (such as this webpage), which requires access to ESI (that's the new API) is bound to the developer license agreement. It's a pretty lengthy document but in order to know that I'm not allowed to access your information without your knowledge and consent, just read section 2.3.