To route mail to ArcTitan from G Suite, first you must set up a Host Route.
In your G Suite console, go to Apps > G Suite > Gmail > Advanced Settings > Hosts, and add a new Host, pointing to your ArcTitan server on port 25:
Once that is created, you will need to create a Route, under Apps > G Suite > Gmail > Advanced Settings > General Settings, adding the X-Gm-Original-To header.
In addition to that, you must add a recipient to use that Host Route that we added earlier, and setting it to firstname.lastname@example.org (or whichever server you are on):
After that, make sure to save your settings. Mail coming into your organization will now start getting sent to ArcTitan as well, and will be searchable shortly after.
See below for details on setting up journaling on gmail