What is the format of the archive files? Is each folder a single file without an extension, i.e. and mbox file? Or a set of eml files? If you saved a TB profile folder, the mail would be stored in mbox files. But if you saved the mail to an external location, they would probably be eml files. Either way, they can be viewed in TB without any additional add-ons or tools.

sfhowes, I have attached a pic of the pertinent file structures. Recall, I just need to be able to view the old POP3 email archives. I hope to be able to delete the old email ID's since Thunderbird tries to connect to them, generating errors. The old ISP no longer exist...

Any specifics as to how to do this is appreciated.

In the Archives folder, copy the mbox files, 2016, 2017, 2018, 2019, into Mail/Local Folders of the active profile, renaming if necessary. Same with any mbox files, such as Inbox, Sent etc., in the ImapMail subfolders. When you restart TB, folders with the same names as the mbox files should appear under Local Folders in the Folder Pane. Once there, you can create new subfolders and move the mail around as needed.

sfhowes,

Thanks! that worked. At first I copied the Archives.sbd folder under "Local Folders". That didn't work. I copied the 20XX, 20XX.msf pairs directly under the "Local Folders" and "viola!" they appeared after the restart of TB, just as you said they would.

I'm glad to hear that, but in future note that it's not necessary to copy the .msf files, as they are automatically recreated when TB restarts and recognizes the mbox file. If the folder contents don't look right in TB, close TB and delete the .msf files.