Do you regularly compact folders (right-click → Compact) to reduce storage space?

You can also go to top menu bar -> File -> Compact folders

Copy Local Folders to another location, then restart TB and Browse... the Local Directory in Account Settings to the new location.

https://kb.mozillazine.org/Moving_your_mail_storage_location_-_Thunderbird

Thanks ThundaMike. Yes, I periodically compact the folders and Thunderbird is still one of the highest users of disk storage. I just don't understand why Local Folders need to be in the same location as the account folders since they are not connected to any account.

Thanks ThundaMike. Yes, I periodically compact the folders and Thunderbird is still one of the highest users of disk storage. I just don't understand why Local Folders need to be in the same location as the account folders since they are not connected to any account.

They are in the same location by default, for convenience. But as sfhowes points out, there is a process you can use to move Local Folders.

Note: not mentioned in the KB article - moving Local Folders may invalidate a message filter if it points to a folder in Local Folders.

Thanks sfhowes, I performed the actions described but was left with an odd situation, To test the new location I added a new local folder in Thunderbird and copied an email to it. When I checked the folders in the new location (NAS drive), the new folder was not there. I looked in the previous location listed in account settings and it was not there either. However, the folder and email can be viewed in Thunderbird. I verified that the account settings for Local Folders was still pointing to the new location. Then I noticed that not all folders were copied to the new location when I did a drag and drop. I am certainly confused and, for now, I have reset the Local Folders location to the original one,

There was an issue related to local folders on network drives that might explain your finding:

https://support.mozilla.org/en-US/questions/1512216