This article addresses an error with the following diagnosis:
-yahoo sent items not syncing with Outlook
1. The main problem is that I connected to Yahoo mail through Outlook 2010. Everything is good but the Sent folder never gets synchronised.
2. I understood later on that my connection was using the POP setting, which does not support sent folder sync.
3. The internet search results talk about changing the whole connection setting into IMAP. The IMAP obviously supports the Sent Folder Sync.
4. Here was the problem. It never worked. Every time I change the setting to IMAP, it gives out error messages that connection to the server failed.
5. I got the IMAP settings from the internet and tried and tried but it never worked.
6. Today, I did something crazy. I changed the setting and it miraculously worked!
The picture shows you the settings. Hope it works with you as well.