first, it is IMPOSSIBLE for an account to switch from IMAP to POP on its own; doing such requires creating a new account in the other protocol. second, thunderbird warns to not exceed 2 gig in creating zip files. if you need to unzip, you might use the free 7-zip at https://www.7-zip.org/ I encourage either doing that, or , if the original setup is still available to just do a simple copy. that is ALWAYS the best approach. that would b

1. exit thunderbird
2. copy the thunderbird profile at c:\users\<yourid>\appdata\roaming\thunderbird to external media
3. install thunderbird on new PC and then exit
4. then, copy the backedup thunderbird folder to c:\users\<yourid>\appdata\roaming to overlay the existing folder and files
5. then, restart thunderbird

Thanks for taking the time to reply, David. I know that the settings changed from IMAP to POP, how I don't know, it doesn't matter at this stage. Also, a warning did not pop up. Will the www.7-zip.org option work on my Mac? and as for step no. (3), does this mean I have to install Thunderbird on a different computer? cheers, Alison

Thanks for taking the time to reply, David. I know that the settings changed from IMAP to POP, how I don't know, it doesn't matter at this stage.

Actually it does. Quite a lot really. It is impossible for anyone trying to assist you in recovering to offer well considered advice. Either they simply do not believe the impossible, which would be me and I think David, in which case you will end up quite frustrated that no one actually believes you. Or they will be missing critical information and start the diagnostic process based on a complete fallacy. Again you will be very frustrated because no one is truly helping solve the problem.

Now lets look at what you have actually said.

You have a Zip file that is by any measure huge, some 6Gb in size. My understanding is there is no limit on the size of a zip file in the apple world. But as I do not play there I really do not know. This discussion would indicate the Apple product should read the zip file natively. https://support.apple.com/en-hk/guide/mac-help/mchlp2528/mac

"Unable to expand 'Thunderbird_profile_backup.zip' into 'email backup 2024-10-18'. (Error 1 - Operation not permitted)."

The first google result I got on that error was where the most likely in my view suggestion was the file is corrupt. This would be consistent with the other error messages you posted. Essentially the file you created is corrupt. A leading cause of file corruption in the zip world is antivirus products. Do you have one? They are very good at corrupting and preventing the copying and expansion of zip files all in the name of "protecting you".

So now can we back way way up to the beginning where I do not believe the story the account changed it's type. I am not interested in trying to recover a corrupt Zip file. That is not something this forum nor it's members really have an expertise in. I see suggestions online that winrar and DiskInternals ZIP Repair may offer repair functionality. But I certainly have no expertise in that.

Goto the help menu for Troubleshooting information. About two thirds of the way down the first block of information there is a show folder button for the profile folder. Click it and you should be dropped into finder in you Thunderbird profile folder.

Navigate to the mail folder (where POP mail is stored in a folder named after the mail server. Do you see your account listed there?

Now try the ImapMail folder, is your account shown here?

The actions to take to recover mail is very different for both of these scenarios, so please post beck you results of the folder that contains your account.

Also, a warning did not pop up. Will the www.7-zip.org option work on my Mac? and as for step no. (3), does this mean I have to install Thunderbird on a different computer? cheers, Alison </blockquote>

Thank you for your reply, Matt. I'll run through the steps you've suggested and report back. I should mention that, yesterday I was on the phone with my ISP support team because Thunderbird had stopped receiving e-mails. During this session, we changed the Thunderbird email account settings back to IMAP. It was before we took those steps that I exported the Thunderbird emails into what now appears to be a corrupt file. As it happens, my anti-virus is currently offline (another trouble-shooting issue high on my list), so that did not interfere with the process. I am sorry that if it appears that I am being difficult or uncooperative in any way. It's just that I specifically recall setting up Thunderbird with IMAP two years ago. regards, Alison p.s. Thank you for the links to Apple: I had seen the first, but not the second which seems germane to the problem.

Hello again. I have opened the Thunderbird profile folder as instructed, then navigated to the Mail folder. This folder is 5.88 GB. My account is listed there, with the most recent activity occurring on Fri. Oct. 18 at 1:31 p.m. That date stamp shows on the Inbox.msf file. Then I also navigated to the ImapMail folder, where my account also resides. This folder is 116.8 MB. The earliest date stamp there is yesterday, Fri. Oct. 18 at 1:32 p.m. This date stamp shows on the mail.[ISP].com.msf file. I have to say that, looking at the relative file sizes, and the first having contained 10-1/2 years of e-mails (compressed periodically, when Thunderbird prompted), this e-mail account must have been set up as POP. I do apologize. It appears my memory went frzzzzt. Does this information help in any way? cheers, Alison p.s. I used the information from the second Apple link you sent, and managed to extract the profile folder. The output identifies things like "bad zipfile offset."