I am trying to do this in Gmail.
I found this:
Request a read receipt
Compose a message as usual while using the desktop version of Gmail at mail.google.com.
Click the More options icon in the compose window.
Click Request read receipt.
Send your message.
Read receipts - G Suite Administrator Help - Google Help
I tried to do that. My "More" options does not have that capability, see attached.
What can I do to enable it.
PS - EE REALLY needs a gmail category. It is used by I'd guess 100 million people.