If you use the same contact for multiple domains, a one-time verification is sufficient—both for confirming the email address and for verifying name and address.
All further domains using the same contact are automatically considered verified, as are future new registrations made with this contact.
Please note, however, that some registries carry out verification independently and may send their own requests. Therefore, despite successful verification with INWX, further verification requests may still occur. In this case, the domain owner will receive a corresponding email from the registry.