How can I get the raw text of an email in iOS Mail?
OK. I think I've got this figured out.

First, you need to have access to a gmail account. Great if the original email is already address to one. Otherwise you'll need to forward to a gmail address (or an account that's accessible via Gmail).

Next, open Gmail in a browser on your iOS device. I used Chrome, but that may not matter. Go to gmail.google.com and sign in to your account. It will likely take you to the mobile version. Scroll down the page and you should see Mobile | Older version | Desktop. You want Desktop.

Once there, open the email in question. Just under the address info for the email, you should see Reply, Reply all, Forward.... Show original. Click Show original and you should be golden.