Quoting David MacQuigg <dmq(_at_)gain(_dot_)com>:
What people do you have in mind? I am thinking about people who operate
public mail servers. If they don't understand a simple reject message
("Sorry, wrong number.), they shouldn't be operating a public mail
server. If they can't fix the problem themselves, and they can't afford to
pay someone to fix it, then they can't be serious about wanting to operate
a public mail server. Private mail servers can go do what they want, but
operating a public mail server should be a public trust. Anyone who abuses
that trust does not deserve out sympathy.
"People who operate public mail servers" -- especially the very large ones -- do
not sit between their users and their users' correspondents' servers,
explaining and handling bounces and rejections for them. Instead, the
confusing responses are most often delivered directly to non-technical end
users.