There may be a simpler way, but this is my way:

- exit thunderbird - locate the archive in your profile and COPY (not move) to your other drive. Ignore the msf - restart thunderbird and click account settings and copies&folders and change to location for archive to the new location - at that point, thunderbird may close and restart - if satisfied with results, you can then delete the original archive location - to backup:

1. ensure thunderbird is not running
2. enter %appdata% in search window on task bar and press Enter key
3. this should open windows file explorer in Appdata\roaming folder
4. highlight the Thunderbird folder and copy to external media
5. copy the external archive from its location

Thanks, David. I will try this.

Hi David, Thanks so much for the advice. Unfortunately I've hit a snag. I have executed the first part of your instructions, copying my Thunderbird archive to my data drive, and to my backup drive as well, but I ran into trouble when I restarted Thunderbird and clicked account settings and copies&folders as you instructed. I was not given the option to change the location for the archive to my new location. Under "Message Archives" my choices are "Archives" Folde on:" and "Other". On "Archives" Folder it's a choice between SBC (which is no longer an active account), Local Folders, or Blogs and News Feeds. I don't seem to be able to specify my D drive. The "Other" alternative is 'Archives on Local Folders", which has a dropdown menu including "SBC", "Local Folders" and "Blogs & News". Below this dropdown menu I see "Archive options" but that's just choices about how the folders should be organized.

I'm wondering if I have a different version of Thunderbird than the one you were referring to. I hope I have given you enough information - I feel like I'm very, very close to solving a major problem. Hoping you can help! Thanks so much!

My sincere apologies. I forgot one thing: you must move ALL local folders to the external drive. I do apologize for the oversight. If still a desirable strategy, copy all Local Folders (again, with windows file explorer and thunderbird not running), and then click account settings, click to Local Folders, and then change location pointer to the external drive. thunderbird will restart, and at that time you can select to store archives in Local Folders.