🚀 go-pugleaf

user@relay!host is not defined.  That is to say the  address is illegal because
it is ambiguous.  At least to me :-).  What do you really want to do?
A ! on the RHS of a @ is undefined.

I'm a good sendmail reference.  There are others :-).

host!user@relay is defined ... means send to relay and relay sends to host for
user.

If you want to send uucp to relay then to user on relay from a uucp host
usually we address it as host!relay!user and host recognizes that relay is
an IP connected node.  In fact since a hostname  should have a domain
it is easy to get the uucp host to recognize that host.domain!user should
be changed to user@host.domain.

But you still cannot have an address with a ! as the right-most operator
end with a hostname.

f