Google Workspace admins can use the Email Log Search feature to inspect emails sent and received by Gmail. However beware that the email detail page isn’t consistent: it can change depending on which filters were used to find it.
If you filter by sender email address, the email detail page shows the correct recipients (including those added by Gmail’s default routing rules).
However if you filter by recipient, the email detail page is the same except the additional recipients aren’t shown.
This is quite confusing.
There is a note in the docs that describes something similar:
Ultimately, if you’re debugging routing rules then always search using the sender address, not the recipient.