I previously used a service that sent me Slashdot articles as individual e-mails. All I had to do was give them the RSS url, and they handled the rest. On the Gmail side, I simply made a filter, labeling these e-mails as News. Once I stopped using the service, I realized that I had more than 20,000 such e-mails stockpiled. While I could delete all News e-mails, there are some that I've forwarded to friends, sometimes receiving multiple replies. These conversations are valuable - I would like to keep them. As far as I can tell, there's no way to search for conversations that have more than one e-mail in the thread. Up until now, I've been deleting them page by page, carefully de-selecting the conversations that have more than one e-mail; however, it will take far too much time to complete. Is there an easier way that I'm missing? 
How can I search for Gmail conversations that have more than one e-mail?
gmail;gmail search;gmail conversations
I have a similar situation where I email a lot of things to myself from Google Reader, I can filter the ones that I have forwarded though by using the to: field.In this case:google reader to:!meWhere the ! mark finds all emails sent to NOT me.Then you can label these and filter again:label:News !label:KeepThis will find all News NOT with the label Keep.