I thought that Yahoo!'s webmail lost the ability to forward emails as attachments long ago.
That was an option once. You could select to forward emails as an attachment or as inline text. I wish that option was available still.
From: "les d's" <lesdsz@yahoo. com>
To: Y-Mail@yahoogroups. com
Sent: Tuesday, June 23, 2009 7:08:27
Subject: Re: [Y-Mail] Re: Where is "View Source" for message content?
I guess one way you can do this to forward the message as an eml attachment, you could then save this eml attachment and open it in thunderbird.