[Exim] Lsearch Questions

I have a config file that has the following line

sender_reject_recipients = @@lsearch*;/usr/local/exim/blacklist.txt

and the blacklist.txt has (shortened :-) )

pixi.com: nlcar
yeah.net: *
earthlink.net: *
sex.com: *
wotch.com: *
protectingyourfiles.com: *
artmarket.com: *
edacafe.com: *
pages.wotch.com: *
helpfuloffers.com: *


The Exim web pages says about * after lsearch as

"If `*' is added to a single-key lookup type (for example, lsearch*) and the
initial lookup fails, the key `*' is looked up in the file to provide a
default value"

Now the questions

1). Am I right in assuming that the blacklist files should have a
    * <somedomain>: <something>
    entry at the end/top for the lsearch* default to work.
    (all the entries in the file are like the about, no * on it's own)

2). I can't find any info on the two @@ at the start of the lsearch,
    What do they do ?

Thanks in advance

Leigh