[Exim] custom SMTP error messages

Hi there,

I'm wondering how I can tell people about temporary problems during mail
routing. AFAICS exim just gives a "Temporary local problem - please try
later" for routing problems, like DNS failure, Database failure,
misconfiguration, etc.

I.e. I'd like to give the "lowest numbered MX record points to local
host" message, that is logged for domains that point to the local host,
and are tried to be routed via dnslookup. I looked at the "self" and
"cannot_route_message" directives, but I can't tell how to distinguish
between non existent / unrouteable domains and misconfigured local
domains...

Any ideas?

TIA,
daniel