Recently, Yahoo instituted the "conversation" schema in the Yahoo! Mail service.
Fortunately, you can disable the "conversation" mode for both. Here is how to do it.
Gmail
- Click the settings icon on the right-top corner and then select "Settings"
- Look down the page a little and find the"Conversation View" setting.
- Click on the "Conversation view off" radio button
- Scroll down to the bottom of the page and click the "Save Changes" button
Yahoo
- Click the settings icon on the right-top corner and then select "Settings"
- On the left, select "Viewing email"
- The top choice will be "When viewing message lists" and to the right there will be a checkbox labeled "Enable conversations"; make sure that checkbox is not checked on.
- Click the "Save" button at the bottom of the panel.