[exim] Routing manually falling back to dnslookup

Okay, I have an outgoing mail server, cortizone, which does mysql
lookups from a separate machine, codeine. I have this in the configure
file on cortizone

our_routes:
   driver                = manualroute
   domains               = +our_domains
   host_find_failed      = defer
   route_data            = codeine.yoafrica.com
   same_domain_copy_routing
   transport             = remote_smtp

The our_domains is as simple as
domainlist our_domains = ${lookup mysql{ALL_DOMAINS}}

This works fantastically until the mysql server falls over. Then I get
these messages in /var/log/exim/paniclog
2005-05-04 16:06:35 1DTHjp-00077A-Es failed to expand "${lookup mysql{SELECT DISTINCT domain FROM relay_to_domains WHERE domain='${quote_mysql:$domain}'}}" while checking a list: lookup of "SELECT DISTINCT domain FROM relay_to_domains WHERE domain='bonbon.net'" gave DEFER: MYSQL connection failed: Can't connect to MySQL server on 'codeine.yoafrica.com' (61)

How do I set it up, so that if the mysql server is down, it does a DNS
lookup and ignores our_routes and our_domains?

-- 
John Oxley
Senior Systems Administrator
Yo!Africa
E-Mail:    john@???
Tel:       +263 4 858404 ext 2017
Cell:      +263 91 335 109