Hi Terry,
You should not have to do anything to activate the surbl checks.
I assume that you have not modified the stock Exim4U /etc/exim/exim.conf and /etc/exim/exim.pl/exim_surbl.pl files. Nevertheless, you may want to verify the following values in etc/exim/exim.pl/exim_surbl.pl since this is where the lookups could be disabled:
my $surbl_enable = 1; my $uribl_enable = 1; my $dbl_enable = 1;
The surbl/uribl/dbl services sometimes refuse lookups from name servers that perform a large number of lookups such as hosting providers and large ISP name servers. I therefore recommend that all mail servers have their own caching name server. You can easily setup your own caching name server with bind/named whereby all of the lookups originate from your IP address instead of a hosting providers' name server IP address that may be blocked. If you have not setup your own caching name server and you are instead relying on your hosting provider or ISP for name services then that could make some or all of the surbl/uribl/dbl lookups fail.
In any event, you should verify that the surbl/uribl/dbl lookups are working properly from your mail server's IP address using one of the testing techniques outlined in section 4 in:
http://exim4u.org/svn/exim4u_src/trunk/NOTES
As an example, test a known blacklisted url in the uribl database with:
nslookup domain.tld.black.uribl.com
If the url is listed then nslookup will generate an output IP address of 127.0.0.2 and the output will look like:
Non-authoritative answer: Name: domain.tld.black.uribl.com Address: 127.0.0.2
Be sure and do the nslookup test from your mail server's IP address. If your test spam's url returns 127.0.0.2 then the url is on the blacklist and everything is working properly. Now, send a test spam email to your mail server that contains the known spammer's link and see if it is rejected. Make sure that you send the test spam from an IP address that is not whitelisted by Exim4U (such as in etc/exim/exim4u_backup_mx_host_names or etc/exim/exim4u_backup_mx_rl_host_names). If the test spam is not then rejected by Exim4U then exim_surbl is indeed not working properly.
If the nslookup is working properly but the spammer url is not rejected then please send me a copy of your test spam email so that I can test and verify it on one of my servers. Be sure and include the entire test email including headers.
Also, as an FYI and for further help, Exim4U's surbl/uribl/dbl blocking simply uses Erik Mugele's perl script which you can read about here:
http://www.teuton.org/~ejm/exim_surbl/#exim
FYI,
Gordon
Thank you Gordon for the very clear and informative reply you were right for some reason my look ups were blocked but setting up a caching name server fixed it straight away.