[Exim] question about DNS timeouts

Hello exim users,

I did search the FAQ but was unable to figure this out:

I have a mail queue on our main routing host that has over 600
messages. Over 95% are error messages relating to spammers and their
"made-up" email domains.

In a nutshell, I'd like to configure exim to try only once or twice to
deliver bounce
messages and then drop them.

I've experimented with different options. I'm currently using:

timeout_frozen_after = 4h
ignore_bounce_errors_after = 1h

The trouble I have is that most of my bounce messages timeout on DNS
lookups
with an error "host_lookup did not complete" and they never get frozen.

I understand that these messages cannot be frozen (and then deleted by
the timer)
because exim doesn't know if they are good or bad.

Is there any way to give up on dns retries in a similar way as frozen
messages
are dealt with ?

Thanks in advance.