Functionality without Google Play Services for Email Providers

I think it would make sense to rate each email provider on PrivacyGuides based on compatibility with degoogled phones, or to add a warning next to those that have sub-par support for degoogled phones. For instance, from what I understand, notifications are supported on the Tutanota app for android without having google play services installed. By contrast, the Proton Mail app requires google play services for notifications to function. This seems important to highlight.