In message , Frank Slootweg
writes:
Mayayana wrote:
"J. P. Gilliver (John)" wrote
[...]

[About Thunderbird's mail storage format.]

All of that's to say that you should be able to
get your email out without much trouble, but I'm
not aware of any program that will just export single
messages. I can drag them out onto the desktop
one at a time, as can also be done with TBird. But
I can't save all of them.

(I - JPG - _didn't_ write that paragraph, though no matter.) [More at
end.]

Elsewhere in this thread, I mentioned Thunderbird's 'ImportExport
Tools' Extension, which *can* export single messages (in .eml format,
which is basically one-message mbox format).

If you export a folder - for example Inbox' - you get a timestamped
(Windows) folder (Inbox_20180917-1808) with a subfolder 'messages' and a
'index.html' file.

The 'messages' folder contains the messages in .eml format, for
example '20180906-Your new F1 hub-2324.eml', where 2324 is probably some
index. You can open these files with Thunderbird and they of course will
have the real Subject: sans fluff, i.e. 'Your new F1 hub'.

You can open the index.html file in your browser, which will show a
list of 'Subject', 'From', 'To', 'Date' and 'Attachment'.

The messages in the 'Subject' column are highlighted/clickable, but
they open the raw/source message. I don't know if that can be changed.

Out of curiosity I tried the
Export function in OE and it told me that it would only
export to Outlook or MS Exchange. Parochial monopoly
strikes again.

Thunderbird (basic, i.e. without Extension) can Import from Outlook
Express and - see above - Thunderbird's 'ImportExport Tools' Extension
can export to .eml or mbox (or HTML or Plain text or PDF or ...) format,
so Bob's your uncle!

FYI, I come from a UNIX and standards background, so I've always
checked if I could export my current mail folders from their proprietary
format to the only real de jure standard, mbox format. That was possible
with Outlook (non-Express) and Outlook Express with third-party software
and with Windows Mail, Windows Live Mail (barf!) and now Thunderbird.

I've not snipped, because all of the above is talking about "getting
your mail out", "import"ing, and "export"ing. I am unaware of any
Windows mail client that _uses_ individual files for emails, rather than
being able to create such files (with or without using extensions). What
I mean is this - if there was such a client: If you examined where the
emails are stored, in Windows Explorer, you'd see folders - named as
they appear inside the client (or at least with a one-to-one
correspondence). If, inside the client, you moved an email from one
folder to another, then looked again with Windows Explorer, there'd be
one more file in one folder and one less in another.

I'm sure there are plenty of reasons why such a client would be
unwieldy, or have similar disadvantages. I do think, though, that if
such an approach had been used from the start (or at least for many
years), such problems would have been overcome as clients developed.
Wishful thinking now, though, as email client development has almost
stopped - certainly nothing as major as that sort of change; the only
changes left happening are minor tweaks, and perhaps protocol changes
(such as encryption implementations, e. g. for passwords).

P. S. - I've just read your post that says WM (and the terrible WLM)
_does_ use single files per email (though you call them mbox rather than
file).
--
J. P. Gilliver. UMRA: 1960/1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

Today, I dare say more people know who starred as /The Vicar of Dibley/ than
know the name of the vicar of their local parish. - Clive Anderson, Radio
Times 15-21 January 2011.