More info may allow for more suggestions. Is the 8gig a POP inbox? Tell us more on the account and where the 8gig is.

The profile has 10 accounts and local folders. Most accounts are POP. Emails go back about 25 years.

Well, I'm not sure moving will improve performance. To keep all accounts active, but with less space, you could archive large components of each and move to another drive and then create a profile to hold them. Or create separate profiles for each account. Easiest way to do that would be to clone the profile by copying the profile in File Explorer with thunderbird not running, and then switch to that profile and delete some accounts and switch back to primary profile and delete the ones in second profile.

The suggestion of having multiple profiles, one for each account is not useful since all accounts are active. I am using local folders to hold history and the plan was to move them to another profile and pass data annually. This would require some option of moving data between profiles. I guess there is no support for this. Thanks for your reply.

Splitting or moving things just introduces more potential for issues IMO. I advise against such measures.

1. With 25 years of mail, surely there is a percentage you can delete, especially ones with large attachments. Be brave.

2. empty all trash and spam folders

3. move everything not currently being worked on or accessed out of account Inboxes and into archives in the account or archives in local folders. see https://support.mozilla.org/en-US/kb/archived-messages

4. do https://wiki.mozilla.org/Thunderbird:Testing:Memory_Usage_Problems