Ignore this. i figured out how to edit my original post. I would delete this if there were a delete button.

Edit: Thank you, MattAuSupport .

Local folders is "an account" so are the other roots in the folder pane.

The open in conversation on ly look in the current "account" for the rest of the conversation.

As I almost exclusively use local folders and POP mail accounts to the Global inbox I have no issues as all with open in Conversation on local folders.

There is also the issue of if the other parties to the conversation use a mail client that retains and adds to the references header section. (older Microsoft Outlook for example does not). References is not compulsory. historically Microsoft used a proprietary exchange based system and other mail clients simply dropped it altogether.

If you look at the message source (ctrl+U) you will see a references section that looks like

References: <55602EC0.90405@gmail.com> <556347DD.3020303@mozilla.com>

it is those references that allow the conversation to be created.

Oops that last post appeared after I clicked Reply. About 5 hours late :(

What is your original question please? The forum is only showing this against your ID and I need to cross link so I can close this permanently.

Hello, Matt. Thank you for your effort.

The screenshot upload failed and I posted the Addendum to get both screenshots in.. I noticed that my filenames were redacted, so when I found out how to edit the original post I replaced the shots with labeled images.

You hit the nail on the head."View Source" shows no reference headers.

[edit start] Not so. My error. See: "Open in Conversation" works on received messages in local subfolder dated 6/5/2015, does not work on other messages in subfolders. https://support.mozilla.org/en-US/que.../1065805 [edit end]