[Exim] make sender_verify warn rather than reject

All

I am trying to make the sender_verify in Exim 3.36 warn rather than reject.

We're finding the number of addresses we are unable to verify is quite high
and this has proven to be tremendously successful in cutting down UCE.

Unfortunately there are a handful of mail servers out there that fail to
accept the null sender "bounce" message, resulting in some "false
positives". This has caused significant heartburn with some of our clients.

If there is a way to make sender_verify "warn", like we can with the RBLs,
then we should be able to find a way to use the system filter or
Spamassassin to rewrite the subject line as **Probable Spam** and let the
clients deal with it their way.

Am I overlooking the obvious?

Relevant conf below.

Bruce C

sender_verify=true
sender_verify_reject=true
sender_verify_hosts_callback = --snipped --
sender_verify_callback_domains = --snipped--
sender_verify_fixup = true