If you used Apple to sign-up to Mob, you may have created an account using your Private Relay Apple ID (aka 'Hide my email').
If you can't recall which email address you used, it may be this encrypted email address (it will follow this format: '[email protected]').
On your iPhone or iPad:
Open the Settings app, then tap your name (first button on the page) to view your Apple ID settings
Tap 'Sign in with Apple'
Tap 'Mob'
You'll see your Relay Email under 'Hide My Email'