FluentSupport Inbox Replies Do Not Thread Properly in Email Clients

Hello,

We have noticed that FluentSupport inbox replies currently do not thread very well in real-world email usage.

When an agent replies to a ticket that originated from an incoming email, FluentSupport sends the outgoing email with an incorrect In-Reply-To header.

Instead of using the original ticket message_id, the header is populated with the sender identity / email address format, which causes the reply to be treated as a new conversation in email clients instead of staying inside the same email thread.

The correct original message_id is already stored in the ticket record (fs_tickets.message_id), so the required data is available.

We also tested a custom fix via hooks, and once In-Reply-To and References are set to the ticket's original message_id, threading works correctly in Gmail both for the recipient and for archived copies.

So the issue does not seem to be missing data. It seems to be the way FluentSupport builds outgoing reply headers for inbox-originated tickets.

Could you please clarify:

1. Is this current behavior intentional?
2. If yes, what is the reason for not using the original ticket message_id in In-Reply-To / References for inbox email replies?
3. If not, do you plan to correct this in core so replies behave as proper threaded email replies in mail clients?

This matters not only for internal archives, but also for the customer experience, since recipients naturally expect support replies to remain in the same email conversation.

Thank you.