[blastrock]

You are right, you'd still have to trust the webmail/chat provider if you want to chat securely. Tanker still protects against data leaks from the app servers in this case.

We also provide SDKs for Android and iOS. They protect against more threats as you can install an app you know the provenance and the app doesn't auto update like a website that you reload every time you open your browser. If you are concerned about security, you could even compile the apps yourself in this case.