How to copy email from one Thunderbird INBOX to another

No idea what happened, but the INBOX folder in my Thunderbird email client lost everything.  All of the subfolders are just fine, only the INBOX was lost.  The emails that disappeared locally also disappeared at the IMAP server.  I have spent two days with every "fix" known to man and cannot get the old emails back.  But I have a copy of the old INBOX folder that is 100X larger than the current / new INBOX folder.  I have looked at both files, and certain the bigger file has the old emails.  I have tried all sorts of swaps, etc, and Thunderbird never likes it.

So what I want to do is copy all of the copy / old INBOX data into the new one.  Will that work?  If I do it, do I need to delete the INBOX.msf folder so Thunderbird will rebuild it?  Anything else to be careful about?
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Mike CaldwellConsultant to IP industryAsked:
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arnoldCommented:
I think the only plausible explanation is that you deleted your inbox and the IMAP server does not have a protection against deleting "protected" folders.  Do you have a web based access to where your email is stored in hopes that the inbox is still in the deleted items folder. If your thunderbird account settings are such that it is set to purge deleted items on exit, those messages are gone.  Checking with the provider who might have backups and might be persuaded to restore your data..........

IMAP usually only stores message headers and is temporary. The difficulty in that is that as soon as you attach it to a thunderbird an IMAP would require a synchronization of the mailbox with the server.

You could try to create a new account and use a copy of the backup inbox as the data of this new account.  See whether you can access the data without loging into the IMAP server possible, configure the account such that it never checks for email.  If you have the data accessible (headers and message body), you might be able to export the messages which you could then try to import.......
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Mike CaldwellConsultant to IP industryAuthor Commented:
I checked the server using webmail two days ago, and the INBOX email was gone.

Had not thought about setting up a new account, then exporting the data, then importing.  I'll think that through a bit and try it in the morning.  Thanks Arnold; sounds plausable.
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arnoldCommented:
Check the deleted items folder to see whether the inbox or the messages are there.
 No matter the IMAP server or the mail delivering incoming email will recreate the inbox if/when missing.
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Dave HoweSoftware and Hardware EngineerCommented:
could also be a corrupted index file on the inbox (the msf) - while Thunderbird is not running, try moving the old inbox file to Mail\Local Folders (within the Thunderbird profile) and renaming it to "old-inbox" - it should turn up under local folders, in Thunderbird, with its new name, when you next open Thunderbird, and will re-create its index.

Further, Thunderbird mailboxes are in mbox format, which is human readable - try opening the mbox file in a programmer's editor able to handle large files (such as VIM) and you can search to see if the missing messages are actually there.
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Mike CaldwellConsultant to IP industryAuthor Commented:
Deleted the MSF file days ago; no change.
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Mike CaldwellConsultant to IP industryAuthor Commented:
I set up a new IMAP account and it won't recognize the saved INBOX file.  What would be great would be a file converter that would take the INBOX file and convert it to MBOX so I could just import it.
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arnoldCommented:
You can not use an IMAP account when attaching a copy of an INBOX since an IMAP type account will necessarily try to initiate a connection to the server to sync the inbox to what is on the server, you do not want the IMAP sync process.
you could try a POP3 account, but do not connect to the server. you just want thunderbird to access the files within.
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Dave HoweSoftware and Hardware EngineerCommented:
imap is fussy about mailbox files - which is why I suggested moving it to the local folder (which isn't :)
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Mike CaldwellConsultant to IP industryAuthor Commented:
Fond a way, actually pretty simple, just had to think it through.  Thanks to all; each contributed a piece of the puzzle.  The solution was this:
1. Make a new POP3 account.   I tried an IMAP account, and as suggested, it did nothing.
2. Copy the old backup IMAP {INBOX} (no extention) into the POP3 account INBOX folder.    Presto, they show up.
3. The easy part: just select all, then "Move to" my IMAP account.  After a couple of hours I have 13K emails copied over and sync'd with the server.
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Dave HoweSoftware and Hardware EngineerCommented:
yup, but didn't need to create a pop3 - local folders would have worked too :)
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Mike CaldwellConsultant to IP industryAuthor Commented:
I didn't notice that nuance Dave.  Makes sense.
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