I see, I think that's so that sender spoofing can't happen.
Try creating a .user.ini file in the root directory of the domain. In it, and in it put:
sendmail_path = "/usr/sbin/sendmail -t -i -f [email protected]"
(using the correct path for your PHP version)
-t Reads the recipient from the headers, -i ignores lines with just . and -f sets the envelope sender. This is the flag that should change the address in the header being sent,
Also see this in the DA Changelogs, this may help also. This is the article on the new anti spoofing features
DA Docs