When a customer sends us an email asking for a quotation, Odoo creates a lead/opportunity from this incoming email. Later, when we generate a quotation from the opportunity and send it by email, Odoo always starts a new email thread with a new subject and message ID.

What we actually need is:

1. Customer sends an email request → “I need a quotation for X sofware.”
2. We create an opportunity and then a quotation in Odoo.
3. When we send the quotation, it should go as a reply to the original customer email thread, not as a completely new conversation.
4. Customer can then reply to approve the quotation → “I confirm.”
5. We can again reply in the same thread → “Thank you, here is your invoice.”

Currently, Odoo sendings the quotation as a new independent email.

Question:

How can we configure Odoo so that the quotation email is sent as a continuation of the original customer’s email (same thread), instead of starting a new email conversation?

Ideally, wéwant to reuse the original email subject and set the proper In-Reply-To / References headers so that the customer sees all communication in one single email thread.