From the backup you made before refreshing your computer. They were on your local drive. If you formatted the drive they are gone.

I backed my data up to an external drive using the File History feature. I did not format that drive, but I can't seem to find the data in the backup drive. Also, with the refresh feature, it does not format the drive I don't think. It retains all the documents. Does anyone know if Thunderbird retains copies of emails for any amount of time? If so, how do I get those?

Thunderbird is software running on your computer. It is up to you to maintain and backup your email.

Have you checked with your email provider to see if copies of your email are still on the server?

I guess I thought I was maintaining it with the File History feature. I think I just found a reason to quit using Thunderbird and use something like Yahoo instead. I don't think my email provider saves more than 2 weeks of emails on my server but I will check.

Thanks

Thunderbird is email client software. Yahoo is an email provider. You might want to learn more about email and how it works.