Voicemail email server IP address block or cert subject name?

I am trying to make sure that messages that come from your voicemail email server...

1. don't get spoofed and

2. don't go into junk or quarantine. 

3. don't get blocked.

Since a user has two choices, receive the emails or don't, I want to make sure that if they ask to receive the emails that they actually get received in their inbox, and not in their junk or quarantine. I know that part of the issue is that you all changed the email address again to voicemail.goto.com. To do this, I would like to add a connector in Microsoft Exchange for them, possibly for all of your emails that the user has an option of turning off.