Unity voicemail relay to Google Apps

[asmlicense]

Hello, I have deployed CUC 11.5. There is not any domain and internal email server. The company's email server is in Google with comany's domain (orkhan@mycompany.us). I want to relay voicemails to user's email account to google. Can you send me headlines with steps what should I do for it?
Should I change smtp domain name in CUC?
Should I have seperate SMTP smart host to relay?
Should smtp smart host be internal, or can use google's relay service (for ex. smtp-relay.gmail.com)?
Thank you

[D12-]

Yes, We had an exchange server prior to the changeover. 

I believe it only allows one smart host.

Once you are fully migrated over to google from exchange you can switch it to the google SMTP relay.