We are using SLA to send 2 reminder emails and one closure email to customer, and there will be an initial email also which is triggering from the flow before this SLA. So the requirement is to include all these emails trails same like we have it in outlook.
For Example: We got the initial Email from the case and then the next Reminder emails should come on the top of the initial email(just like we have it in the Outlook)
To show the emails as one conversation, send every reminder and closure email as a reply to the first email instead of sending each one as a new message. Store the Message-ID of the initial outbound email on the case when it is sent. In the SLA email step, use that stored value to populate the email headers like In-Reply-To and References before sending the next email. This makes email clients group the reminder emails under the original email, just like an Outlook thread. Keep the same subject line format as well, so the full trail stays together for the customer.