FAQ: How do you send a follow-up (bump) email within the same thread as a previous email?
When setting up an email step in a Flow, you can select the option to include the email in an existing thread. The Include in Thread checkbox ensures your follow-up appears as a response to the previous email in the Flow.
Note: The Include in Thread checkbox won’t appear on the first email in a Flow since there’s no prior email to thread onto, but it will be available for all subsequent steps.