[exim] domainlist mysql lookup not working

I have created a named list populated by a mysql lookup in the general
section like this:

BLOCK_REGEX = SELECT regex_domain FROM whitelist WHERE regex_domain !=
'' AND block = '-1'

domainlist dom_regex = ${lookup mysql{BLOCK_REGEX}}

Then I use this list in the acl_smtp_rcpt like this

deny    message = Administrative Prohibition
        sender_domains = +dom_regex

The row data is regular expressions like ^.*domain1.* ^.*domain2.* etc

But the domain1.com is not found in the list when there is more than one
domain returned by the query. Domain1.com is found in the list if only
one domain is returend by the query, that is the Mysql lookup results in
one domain found.

I ahve also tried this as per the exim documentation.
domainlist dom_regex = <\n ${lookup mysql{BLOCK_REGEX}}

What's the way to use a Mysql lookup to provide a list of domains to a
domainlist?

Thanks in advance.
Craig