Yahoo!’s automatic settings ensure that your messages will remain in the Inbox of your external mail account and NOT be deleted. However, you can choose for them to be deleted from that Inbox if you want.

To set Yahoo! Mail to delete the mail in your other account’s Inbox after bringing it into Yahoo! Mail:

1. Click Options in the upper-right corner of your Mail page.
2. Under “Management”, click Mail Addresses.
3. Click once on the account you want to change the settings for. Then click Edit.
4. Find the "Leave Mail on POP server" setting. It’s in the last category: Options. Click on the box to add or remove the “check”.
5. Check the box to keep the messages in the Inbox of the other account.
6. Remove the check from the box to delete them from the other account’s Inbox.

Done? Be sure to click Save Changes in the lower left to put your new settings into effect.