This approach doesn't work, not even for DJB. For example, take qmail: https://www.abuseat.org/qmailhelp.html https://www.abuseat.org/qmailhelp.html Qmail doe

This approach doesn't work, not even for DJB. For example, take qmail: https://www.abuseat.org/qmailhelp.html https://www.abuseat.org/qmailhelp.html Qmail does late bounces for a very specific reason: since it was architected and implemented long before spam became a serious problem, Daniel J. Bernstein (DJB) implemented Qmail in a highly efficient, but inflexible way. ... Qmail is essentially dead - there is no further development on the project as a whole, users of it are stuck with an old core, and lots of ad-hoc and sometimes conflicting patches. In other words, an obsolete design, and no ongoing coordinated maintenance.