Your private key for email decryption is stored on your device to avoid compromising your privacy. However, to prevent you losing your email data if you lose access to your device, c.Email automatically encrypts a backup key for you. The retrieval process for this key is only triggered when you sign in using biometrics on a new device.
When you first download c.Email, you will be prompted to set a password for your backup. Once you have done this, c.Email automatically encrypts and uploads a backup key to your cloud provider, such as Google Drive, iCloud, or OneDrive.
To recover your data, install c.Email on a new device and choose the email address you were using previously. Once you have completed authentication with your email provider and identity verification with c.Email, you will be asked for your backup password. c.Email will then retrieve the encrypted backup from the cloud and restore your keys.
You can configure this process and change your backup password in your c.Email settings.