I would suggest you seriously consider moving the local folders back to the profile, or to another more suitable location. Documents sees a lot of AV scanning, not something that is conducive to database operations which is what reading the mail folders amounts to.

But other than backing up the user profile you will need to check each account to get the location set for mail storage.

While setting locations for storage per account works, it is prone to disaster as not everyone manages to identify all the locations when it is time for a new box. I really think it is still there for the Old Eudora users who think everything can be fixed with a tweak in notepad. From a support perspective I would love to see it disappear.

Thanks Matt. When you say it is prone to disaster, you mean when restoring data to a new computer, if you don't copy the custom mail storage locations to the exact same directory before copying the profile folder and starting thunderbird, it will freak out and not restore the data? Then do you have to start over again making sure you get the proper locations?

You can fiddle wit the directories until you get it right. Nothing gets deleted, so it would be very uncommon for you to actually loose the data but account directories are absolute locations and in the case on NON local paths they are stored as URL type paths with server names not drive letters.

The biggest issue really is data corruption caused usually by anti virus products, although some have tried using streaming backups on those folders with equally disastrous results.

The bottom line is Thunderbird was modified back about V24 to prevent it accepting "unsafe locations" for profile data, mail being part of that. See https://support.mozilla.org/en-US/kb/dangerous-directories-Thunderbird-account-settings

The real question is why change it to a documents folder in the first place?

Just curious, you say Documents folder sees a lot of AV scanning, doesn't it get scanned the same as any other directory? Doesn't the AV just scan every file read, written to, or accessed with the same signatures regardless of location?