It’s unclear which zone you are using for the configuration: "notification.mygatecorp.com" or "mygatecorp.com". If you are configuring it under the "mygatecorp.com" domain, you will need to modify the DKIM name to "selector1-azurecomm-prod-net._domainkey.azurecomm.net.notification". For more information, you can refer to this documentation Verify custom domain