[exim] DNS list lookup defer (probably timeout)

Hi,
I am using exim 4.51 on FC3.

RBL lookups take a very long time if the ip address is not listed, resulting in, for example:

DNS list lookup defer (probably timeout) for 240.218.158.202.sbl.spamhaus.org: assumed not in list

The relevant section of my exim.conf is:

deny      hosts         = !127.0.0.1
          message       = rejected because $sender_host_address is in a black list at $dnslist_domain\n$dnslist_text
          dnslists      = sbl.spamhaus.org:relays.orbd.org:dnsbl.njabl.org:dnsbl.sorbs.net

www.dnsreport.com on my mailserver reports:

ERROR: I could not complete a connection to any of your mailservers!

mail.mydomain.com: Timed out [Last data sent: RCPT TO: ]

If this is a timeout problem, note that the DNS report only waits about 40 seconds for responses, so your mail *may*
work fine in this case but you will need to use testing tools specifically designed for such situations to be certain.


If I comment out that section in my exim.conf www.dnsreport.com reports:

OK: I was able to connect to all of your mailservers.

I've googled and searched the exim archives.

Is there some way I can fix this?

Thanks,
Kerry.