The actual data is stored very differently. So no there is no move or copy you can do. Seriously 500 plus mail accounts is a rather large number for any import process. to cope with. When I first started reading your issue I went Hmm 64Kb is a common fall over in older programs. (Thunderbird import is old.),

You might get some mileage from Eudora rescue. It has not been updated in around a decade, but it will create mbox file that can be imported into Thunderbird using the import export tools

Thank you. I found archived ancient versions of Thunderbird here http://ftp.mozilla.org/pub/mozilla.org/thunderbird/releases/

and downloaded both Version 1.0, and Version 3.0.11, per this article: http://kb.mozillazine.org/Go_back_to_an_old_version_of_Thunderbird

Reading the "readme" for Eudora Rescue, I'm pretty sure I need to know the path to where Thunderbird stores its mailboxes, as well as what the mailbox extensions are (.mbx?). For example, if I install Mozilla Thunderbird on my E:\ drive, are the mailboxes located in the root directory of E:\Mozilla Thunderbird\  ? Some Subdirectory? And, again, what is the mailbox extension for Thunderbird?

Thanks!

Thunderbird has no file extension. The files are Berkley Mbox, but they have no file extension.

Under windows the root of your profile folder can be located by typing %appdata%\Thunderbird\profiles into the start menu search / run and pressing enter.

I have heard that Thunderbird 1.5 is actually best for importing Eudora, but have no first hand experience. Just a note I saw in Bugzilla.

Personally I would just have Eudora Rescue make some mbox files for me. and use the import/export tools add-on to bring them into Thunderbird. https://addons.mozilla.org/en-US/thunderbird/addon/importexporttools/

Well, I'm getting a WHOLE LOT closer...except, the Import/Export Add-On doesn't execute. I used the Eudora Rescue utility at a DOS CMD prompt within windows, and successfully "rescued" them (whatever that means) into another directory. All of the converted mailboxes have the .mbx extension. Then, I downloaded Thunderbird 1.5, installed the Import/Export Add-on, and tried three different ways to import any and/or all of the converted .mbx files. I select the file (or directory) and click "Open" and nothing happens. The screen just reverts back to Thunderbird's basic screen. Got any suggestions? I notice that the instructions for the import/export state that it will import .eml files. Should the converted mailboxes all be given an .eml extension during the conversion? Or did I miss something far more basic? Thanks!!

HOLY GETOUTTATOWN!! IT WORKED!! Apparently, I was selecting the incorrect "import" option. I finally just selected <ImportExportTools><Import mbx file> and was given several options, so I selected <Select a directory where searching the mbox files to import> and just selected my EudoraConverted directory. Thunderbird only had to think for about 40 seconds, and ALL of the mailboxes popped up. It took maybe another 30 seconds for all of the messages to populate all of the mailboxes. FWIW, the conversion was more than 120,000 messages in 497 mailboxes. And, they ALL appear to have showed up, although I'm still randomly testing. THANK YOU for all of your help. NOW, to upgrade TBird 1.5 to the current version!! Thanks, again! Problem Solved!!

While I mentioned Thunderbird 1.5 for importing Eudora, it is not relevant to importing Mbox files. I think you would be a lot better with the current (or almost current) version. But it looks like the changes to profiles over the years did not trip up the import export tools.

Please install V3 again to update your profile folder then you can more on to a later version.

Matt, Thank you for everything. BEFORE I'd gotten your most recent response, above, I had imported everything into Version 1.5. I then just installed the current version on top of 1.5. Did I lose or miss anything by NOT going from V1.5 to V3.0, prior to overinstalling the current version?

aba42 said

Matt, Thank you for everything. BEFORE I'd gotten your most recent response, above, I had imported everything into Version 1.5. I then just installed the current version on top of 1.5. Did I lose or miss anything by NOT going from V1.5 to V3.0, prior to overinstalling the current version?

The major change was the account password storage, so basically you loose the stored account passwords. Other changes will not affect I don't think as you will have been importing mail, not customizing.