Salesforce Email Items are Truncated in Case Feed When Thread ID is Present (no change required if team prefers current title)

Why Emails Are Truncated in Case Feed

When an email includes a Thread ID (Ref ID) in the body, the Email Feed Item Body is truncated at that point. The purpose of this design is to prevent duplicate content from appearing in the Case Feed: since the Thread ID marks the beginning of quoted text from a prior email in the thread, that prior email has most likely already been created as a separate Feed Item. To streamline the view and prevent duplication, Salesforce truncates the quoted content.
This is expected behavior and not a bug. If customers need to view the complete email body, they can open the original email from the Activity Timeline.