This article contains recommendations and best practices to use if your mail is hosted on Google G Suite.
Create an Inbound Gateway
When you create an inbound gateway, you are telling Google that your mail is processed by MX Guardian before reaching the Google servers.
To create an inbound gateway:
- Sign in to the Google Admin console.
- From the dashboard, go to Apps > G Suite > Gmail > Advanced settings.
- Scroll down to Inbound Gateway
- Hover the cursor to the right of Inbound gateway. To create a new inbound gateway setting, click Configure.
- Under Inbound Gateway, type "MX Guardian Gateway"
- Under Gateway IPs, add the MX Guardian IP addresses which can be found at http://www.mxguardian.net/ips. You need to add each address one at a time.
- Click Add
- Type (or copy & paste) the first IP address
- Click Save
- Repeat for each of the IP addresses listed
- Check the box next to "Reject all mail not from gateway IPs"
- Click Add Setting
- Click Save at the bottom of the Gmail Settings page.
More information can be found at: https://support.google.com/a/answer/60730?hl=en