Show Long Headers
I have tried this but can't even find 'Show Long Headers'. Any ideas?
https://support.apple.com/kb/ph2640?locale=en_US
By default, each email you receive displays the email’s sender, recipients, and date. When using Mail on iCloud.com if you want to see more details about a message—such as an email’s return and delivery paths, “Reply-to” field, and content type—you can display its long header.
View long message headers
Double-click a message to open it in a new window.
Click the Action pop-up menu in the toolbar, then choose Show Long Headers.
After you choose to show long headers, they continue to appear until you turn them off.
iPad Pro iPhone 6+ Ver 12.1.4
iPad Pro, iOS 12