In what app? Generic email, gmail some other email program? It's usually not a protected area. you should be able to just put the cursor at the end of the addresses and hold the back space key down.
Are you referring to the contact that shows up in the forwarding slot? Or an email address that shows up in the body of the text being sent in the email?
If it's the contact on the forwarding box then it should delete by doing what you are trying to do to remove the contact.
Its the email addresses that show in the body of the text that I want to send.
In my Yahoo mail, they show under where it says 'hide original'.
If I touch 'hide original,' everything disappears except the email subject.