This PR updates the email validation regex to better handle use cases with hyphens. Changes: - Disallows domains starting or ending with a hyphen (`user@-example.com`, `user@example-.com`). - Allows domains with consecutive hyphens inside (`user@ex--ample.com`). - Allows multiple subdomains (`user@sub.domain.example.com`). - Adds `int test` coverage for multiple domain use case scenarios.