An easy way I found to see the original email address is to reply to the message and scroll down in the new message until you see the original _quoted_ message. It should start with something like:

> On Mar 30, 2019, at 11:38 PM, John Doe <[email protected]> wrote:

The email address is between the < and > characters. If you don't really want to reply, just touch "Cancel" to dismiss the new email.

As pointed out below by [youcantryreachingme](https://apple.stackexchange.com/users/163666/youcantryreachingme), this only works for the sender. If you have multiple email addresses associated with the same email account, it will not reveal the address that the email came in on.

I found an alternative approach though that does appear to show everything:

1. View the message
2. Touch reply button
3. In the action sheet scroll down to Print
4. In the Printer Options screen use the two-finger zoom gesture on the image of the email
5. In the new preview view, you should see all of the email addresses taken from the original email

[![enter image description here][1]][1]


  [1]: https://i.sstatic.net/OdaZG.png