How to see emails that were bounced off the yahoo email

I don't think you'll get any direct information out of Yahoo! as that would potentially give spammers an edge in the never ending war between the spammers and spam filters.

Have you analysed the headers as received by the Yahoo! account? They might contain some information inserted by the spam filter.

Other than that, contact Yahoo! and explain the situation. They might be able to add your domain onto their white list.

After posting my question I came up with the following:

1. Search for messages from a particular sender. The result will be Yahoo displays only messages from that sender. In effect, you are subsetting your email to only those from that sender

2. Then select 'unread' under the square symbol (to the left of the trash can icon). That will select unread messages from the specified sender, but not unread messages from other senders not specified in Step 1.

3. Now click on the trash can icon. That will send messages selected in Step 2 to the Trash folder.

4. Note that only the first 100 messages selected in Step 3 will be sent to the Trash folder. Highlight the Trash folder with your mouse cursor and click on the trash can icon that lights up as the Trash folder lights up. This trash can icon is different from the trash can icon mentioned in Step 2.

5. You will be asked whether you want to empty the Trash folder. Click 'okay'.

You will have to repeat this process if you want to delete more than 100 unread messages from a particular sender.