Swipe left on the preview pages to view all the pages of your email. Optionally, you can tap the Range field on this page, and select a page range to copy. This might be useful if you don’t want to copy all the pages of the email.

On some versions, you may have to long-press on the page preview instead of pinching out with two fingers.

You can then paste the email and all of its pages to Notes or an email or text message.