I wish there were more information on how data is accessed / stored. The site claims that the only thing that is stored is the email address of the user, the re

I wish there were more information on how data is accessed / stored. The site claims that the only thing that is stored is the email address of the user, the rest lives in gmail. Is there an app that can read all the email and then store metadata back into each thread ? Can this app 'tee' my data somewhere else without me knowing? I guess a lot of people are not excited to give anyone else access to their email.