I have been sitting on this question for ages, because I have had similar problems (long ago now) when I was moving between email clients.

I don't have my fingertips on a solution, if one is still needed, but here are two approaches that might work:

1.  Stand up a mailserver (there are some very simple ones), and use that to import your mail into Thunderbird.  This may require converting your mbox file into something else, but this is an old problem that has established tools.

2.  Figure out what format Thuderbird wants to store mail in, convert that, and move it into the expected place for mail in the filesystem.  This may require rebuilding an index for your mailbox, but the last time I used Thunderbird it wasn't hard to do that.

Good luck!

On Sat, 13 Feb 2021 at 13:52, William Park via talk <talk@gtalug.org> wrote:

I'm beginning to like Thunderbird.  It replaces fetchmail, procmail, sendmail, mutt, and vim for mailing.  I miss vim, though.

Now, the question on hand... I have lots of "mbox" format files of old emails.  How do I import into Thunderbird?  Online talks about "Import MBOX file" under "Tools".  But, mine (68.12.0) don't have such entry.

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