[mythtv-users] Posts from digest subscribers

[Jan Ceuleers]

On 17/05/2020 17:08, Barry Martin wrote:
>> So a few lines summarizing what to do would be most appreciated, EG I always thought that keeping the reply intact maintained the thread.
> 
> I don’t know either, which might be a good thing as we’re being the
> vocal portion of the Group Who Does Not Know – probably the majority of
> the posters other than those giving us answers to our questions.

For an excellent illustration of what threaded email lists look like,
visit the following mythtv-users archive link, which shows the May 2020
posts in threaded format:

http://lists.mythtv.org/pipermail/mythtv-users/2020-May/thread.html

This shows which posts were replies to which other posts, in a tree-like
arrangement.

You asked about how this works -- here goes.

Each email (whether it is sent to a list or not) contains a "Message-ID"
header. Most email clients hide the headers by default. I use
Thunderbird, and the incantation to get it to display the headers is Ctrl-U.

Here is the Message-ID header extracted from your email (i.e. the one
I'm now replying to):

 Message-ID: <d3aeeb03-94c1-8722-6792-76e71d238df2 at GMail.com>

(I inserted a space in front to avoid any risk of malfunction)

You will see if you display the headers on the message you're now
reading that it contains an "In-Reply-To" header, as follows:

 In-Reply-To: <d3aeeb03-94c1-8722-6792-76e71d238df2 at GMail.com>

This informs the recipient's email client about the threading
relationships between messages, so that it can (optionally) display them
in a format similar to the one shown on the archive page I linked to above.

In summary, threading isn't done based on subject, but based on the
Message-ID and In-Reply-To headers. A thread can consist of messages
having different subjects.

Hope this clarifies.

Cheers, Jan