The steps outlined below detail how to deprovision a service account for Gmail (Inline Mode) - Inbound Protection.
The Google Drive, Gmail, Gmail (Inline Mode) service accounts share the same Trend Micro Cloud App Security application. If you are still using the Gmail or Google Drive service account, skip this step and step 5.
Go to Google Account > Security > Third-party apps with account access and click manage third-party access.
On the Apps with access to your account screen, click the application named Trend Micro Cloud App Security, and then click REMOVE ACCESS.
For details, see Changes Made Under Inline Protection.