If you are having problems with email messages bouncing (not delivering) in Google Apps, please follow the steps below to add the sending email servers to the whitelist.
1. Log in to the Google Apps admin portal.
2. Select Apps.
3. Select G Suite.
4. Select Gmail.
5. Select Advanced Settings.
6. In the Organization's section, highlight your domain.
7. In the Email Whitelist section, enter the following IP address: