[Exim] local domains from mysql db

Can anyone help me,

I'm trying to set the local domains setting from a mysql database.
I have managed to get a query to work in the director:

mysql_aliases:
search_type = mysql
query = select alias_to from email_aliases where real_name =
'$local_part';
etc etc etc..

.. that works fine, but the local domains setting:

local_domains = "mysql; select domain_name from domains;"

causes exim to think that *every* domain name is a local domain, obviously
causing major problems.

Is there anywhere I can find out exactly how the mysql lookup works, as the
manual doesn't seem to explain it all that well.

Thanks in advance

Gareth Down
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