I tried logging in using my Google account, but I got this:

"Access blocked: tubemail.io has not completed the Google verification process p.c.frankplads@gmail.com

tubemail.io has not completed the Google verification process. The app is currently being tested, and can only be accessed by developer-approved testers. If you think you should have access, contact the developer.

If you are a developer of tubemail.io, see error details.

Error 403: access_denied"