Retrieving values via an unrelated field

Hello,

Let's imagine the following schema and a user table containing an email field.

I would like to retrieve all the information about a user's (in the users table) contract signatures based on the email value in the contract_clients table. What is the best way to do this?

Context: An organisation creates a contract and registers a customer to sign the contract via a signature. Later on, if the customer creates an account and becomes a user, I would like to be able to show him the contracts he signed as a customer.