Copying a thunderbird program from an old computer to a new computer

filters are normally stored within the account. Look for msgfilterrules.dat. BUT, if the configuration is different, you will need to edit the filters. They are simple text files.

What if there was already account info on the target computer? I was setting up a new PC when the old PC crashed, before I could copy the profile. How do I preserve the emails received on the target PC while copying the profile from the crashed PC, using the command prompt?

From your post, it seems you already have a profile on target computer, since you are receiving mail there. Is it that you set up one account and there are others? Please provide more detail and define which accounts are POP and which are IMAP an whether you had folders in Local Folders on old PC as well. Is the hard drive on old PC still accessible? Thank you

Yes, I created the profile as part of the initial setup of the new PC, assuming I could move the data; I didn't know a Windows update would stop the first PC from running. So, I couldn't export the Thunderbird files, just copy via a USB drive. Both email accounts are/were IMAP, but the original kept its files under the folder Mail (it used to be a POP account, which was updated to IMAP), while the new uses a folder named ImapMail. Copying the profile, as above, failed. Also, I've tried to just copy some of the stored mail folders from the original, i.e.: name and name.msf, but Thunderbird just deletes them as soon as it sees them. I was able to import the address books, however.

We're talking old PC: Windows 10, new PC Windows 11, which probably has something to do with it.

I may have found my answer: the files foldercache.json and foldertree.json have the path to each of the local folders from the old PC; I suspect if I add these paths to those files in Imapmail at the same time I copy the folders 'name' and 'name'.msg, they will stay. Hope this doesn't crash Thunderbird and require a re-install.

OK, that did NOT work. After editing the json files with a path to 'name' and 'name.msf' and starting Thunderbird, the folder showed up on the tree, with a message count. But, when I selected that folder, it was empty and the message count dropped to 0.

I am not understanding the full picture. If the message folders are in an IMAP account, thunderbird will automatically populate the folders. If you copy a message folder to the wrong IMAP account, the contents will be deleted. If you copy and place the message folders in Mail\Local Folders they should remain.