[exim] bounce message with hosts_require_tls

Hi!

I created a route and a transport in my exim configuration to allow
certain sender domains to enforce encrypted transfer (mandantory tls).
The idea is that if an authenticated user sends an email, the server
looks up if the domain has mandantory tls enabled and routes the message
through the transport that only succeeds if the remote mail server
supports tls.

That was the easy part. :-) Another part of the idea is that the sender
receives a bouncer if remote server doesn't support tls. Unfortunately
exim seems to handle a failed hosts_require_tls condition as an
temporary error, puts the mail to the queue and tries again and again to
deliver the mail. If the retry timeout is exceeded, the error message in
the bouncer mail is:

"retry timeout exceeded"

instead of something like

"remote server doesn't support tls delivery"

Any idea how to change that behavior so that the sender gets a bouncer
with a meaningful return message?

My config parts are:

# router/150_exim4-config_mandantorytls_route
#############################################
# route for mandantory tls
mandantorytls_route:
  debug_print = "R: mandantorytls_route for $domain"
  driver = dnslookup
  domains = +mandantorytls_domains
  transport = remote_smtp_mandantorytls

### transport/30_exim4-config_remote_smtp_mandantorytls
#######################################################
# enforce tls
remote_smtp_mandantorytls:
  debug_print = "T: remote_smtp_mandantorytls for $local_part@$domain"
  driver = smtp
  hosts_require_tls = *
  tls_tempfail_tryclear = false

Thanks a lot!

Daniel