It may help to see a screenshot of your Imapmail folder and your Mail folder and your Mail\Local Folders folder. That will provide (probably) all the info needed to give you some useful suggestions.

Thank you David. The only screenshot I can figure to send is attached.

thanks. More is needed.

1. do you have any IMAP accounts? if so, a screenshot of the Imapmail folder for each account will show space usage
2. do you have any POP accounts? If so, a screenshot of the Mail folder for each account will show space usage
3. for the Local foders, please do a screenshot for each of the accounts listed.

Those will show clearly where the space is being used and then I can advise what can be done, thank you,

I looked for my iMAP folder and could not find it. I google how to find it and still did not find it.

I'm using Thunderbird 128.2.3esr (64-bit) Safari browser Version 18.0 (19619.1.26.111.10, 19619) Macbook Air M2 15" running OS 14.7

1. click help>troubleshootinginformation
2. scroll down to 'profile folder' and click 'open profile'
3. the imapmail folder and Mail folder should be visible as you are now in the profile.

I found the Profile Folder but no evidence of "open profile". Unfortunately I cannot attached a .pdf file of the Troubleshooting window to this reply, only images.

I use windows. Click 'show in finder' from that screenshot. It may be the same thing

Thanks. When I click on "Show in Finder" I get a window with a folder hilighted (see attachment); and when I open the hilighted folder, I see a list of items (see other attachment). What to do next?