Email issue - Return Path

[eluser]FranckRR[/eluser]
Why CI forces the Return-path = From ?

Because in case of a backend service that send the mail through a sharing, The from is the sender mail, the Return-Path must be the server's mail so it could matche the smtp => avoid blacklisting.
The main goal is to have sender's address via mailer host and the reply-to to the sender's mail.