Close thunderbird and re-open it to see.

Close thunderbird and re-open it to see.

Or collapse the folder list for yahoo by double clicking on the account in the folder pane, and do it a second time.

Thanks all.

I closed the app and reopened the app. It didn't help. Today, I closed the app and didn't reopen the app until a few hours later. Then the sync occurred.

This is quite odd. It seems the sync isn't working correctly in various ways.

Notes: 1. In all these actions, the folders have at least 7k mails. I wonder if this matters (seeing new folder with large# of emails/removing folder with large number of emails).

Thunderbird should at least show new folder names (if not able to add all mails into a new folder right away) according to the configured sync intervals. This way, at least I know Thunderbird is detecting a change.

I wonder if Thunderbird is stuck trying to perform one big task (e.g. trying to add 8k mails to one single folder) and never gets to add all new folder names first.

Perhaps Thunderbird should tackle the sync w top-level tasks first (e.g. add/remove folder names), then do the add/remove mails incrementally for each folder (if such tasks are taking too long to complete).

• • I'd think Thunderbird would want to at least fix the app's sync so I don't have to collapse/reopen the email account's top level tab or close/re-open the app to get sync working.

2. The max mail/folder size it synced still bothers me. This means I can't keep the #of mails in any folder > 8k mails.

3. Syncing is quite fast in Outlook Classic. I wonder the reason syncing is slower in Thunderbird vs. Outlook Classic?

Thunderbird doesn't have a max size.

I'd say something is throttling you. Also, in support circles yahoo's behavior is known to erratic.

Regarding the number of emails downloaded ( your issue 1 ), please verify Synchronization & Storage option to see if any limit was set on it.

Click on Tools and then Account Settings . You'll see that option under your account , the 5th element from the top.