You could select the message you want to forward, and use '''right-click|forward as attachment''', which will create a ''new'' message with the selected message attached. Another way, if you already have a message being composed, is to drag and drop the message to be forwarded onto your new message. Drop it into the addressing area at the top, not onto the message text. And of course you could use this method to add multiple messages as attachments. Note that pretty much any file can be added as an attachment this way too.