This would only be an issue if you had multiple mailboxes on IVM that had recipient e-mail addresses in them that used different domains. The obvious answer for you is register your own domain name, setup e-mail addresses for all your employees in your own domain name, setup the IVM mailboxes to send direct to those e-mail addresses, and setup IVM to use plain, unauthenticated SMTP to deliver mail direct to the host (gmail) that your domain name is on. Since your delivering to the destination mailserver for the recipient address there is no requirement for authentication or encryption.