Hi Rose Holiday,
Thanks for using lunascape.
I suggest you can try this out,
From the outlook mail account, you can set the yahoo mail account as your default email.
Please follow this link for setting up yahoo mail account in outlook.
After setting the yahoo mail account in Outlook Account, please follow this steps:
1. Start the Outlook express.
2. From Tool bar, select Account settings and select yahoo mail which you have set up and set as default.
3. Close the setting screen.
Hope this helps.