Whenever I get a phishing email I forward it to the company that the phisher purports to be....and I provide all the expanded Header details. However, it seems that the Header information cannot be sent easily. I open the Header, which reveals all the details, but when I try to forward it Apple Mail closes the window and reverts to the short header version. Is there a way to have the full header window stay open for forwarding?

I can, and do, copy the Header information and paste it into the email. It's not the end of the world but it is a bit of a pain. Just forwarding would be so much easier and quicker.

I just forwarded a message I had received to myself then opened the forwarded message in raw source. Both my forwarding header and the header from the forwarded message were visible.

Alternatively you could open the fishing message, show it in raw source then select it all (⌘A), copy the selected text (⌘C, then paste the entire thing into the reporting message (⌘V), and send that.

What joemikeb suggests above is what you said you do, but let me add one variation: as suggested, select all of the text in the e-mail, including the expanded header. But instead of copying and pasting into a new e-mail, select to forward it.

I have noticed that you can control how much of an e-mail gets forwarded or copied in a reply by selecting the text you want the reply/forward to contain.

I've been using this technique for years to prune lengthy email exchanges of their increasingly absurd levels of nested quotes.

I've used that method too, but as far as I can tell, it doesn't work with headers.

They apparently can't be forwarded, nor do they appear if I try to print.

That's my experience. I think it's a shortcoming and I don't understand the logic behind it. If we are to fight phishing, we need to give the companies whose names are being used, the best and most helpful information possible.