Currently, there are a few ways how emails can be logged to Timeline:
1. Using Email to Timeline feature using BCC
2. Via Chrome Addin -"Email to Timeline" checkbox
3. Create an activity manually in Timeline
It would be helpful to sync Gmail emails in Gainsight automatically, the same as the "configuring your calendar" feature. Our CSM team suggested this and find this as a quickest way to track conversations in Gainsight