[Exim] failure messages (locally generated)

Failure reports generated by v3 used to say nice things like:

Unknown local-part "xxx" in domain "yyy"

or:

Unrouteable mail domain "zzz"

which gave the user some idea of what's wrong. But in v4 with the unified
directors and routers, using the outofbox config we now get only:

Unrouteable address

for everything. OK - I know the outofbox v4 config has ACLs that give
slightly different responses over SMTP, but here I'm concerned with
locally generated failure reports - either where there are logged-in
users, or where a mailhub wishes to accept everything from (known friendly)
SMTP clients.

So I've been trying a couple of routers to give slightly more detailed
error messages:

unknown_domain:        (comes after manualroute+dnslookup)
  driver = redirect
  domains = ! +local_domains
  allow_fail
  data=:fail:unrouteable mail domain "$domain"
  no_more

unknown_user:           (the final router)
  driver = redirect
  domains = +local_domains
  allow_fail
  data=:fail:unknown local-part "$local_part" in domain "$domain"

Just wondering if this is sensible ? daft ? Anyone know a better way ?

Thanks.

Chris

--
Chris Edwards                   University of Glasgow Computing Service,
C.Edwards@???    Glasgow, Scotland. Phone: +44 141 330 4892.