You can revoke the Sortd's permission to access your email any time you want. Once you do that, it has the exact opposite effect of what you did when you gave Sortd permission when you signed up - Sortd will no longer have the ability to access your mailbox without asking you for permission again. This will also mean Sortd will no longer work as the permissions are required.
Here's how you revoke Sortd's (and any other app's) permission from Gmail:
Ensure that you are logged into your Gmail Account, then go to https://myaccount.google.com/security. This is the main security page for your Google/Gmail account and allows you to change your security settings.
If you find you are logged into the wrong Google account you can use the standard Google Account switcher at the top right to switch to the correct account.
To Remove all permission you gave to the Sortd App, click on “Apps with account access” under "Signin and Security" on the menu item on the left. Then click on "Manage Apps" in the main screen and scroll down until you find Sortd.
Click on the Sortd item and then click "Remove Access".
From this point forward Sortd will no longer have access to your email account at all.
If you'd like to learn more about how apps can access your account, we recommend that you read this Google support article: