On duplicate ignore

Hi,

Ours is a web-based application. We're trying to implement ON DUPLICATE
IGNORE for one of our application table, named EMAILLIST. After a quick
Google search, I'm finding the following "easy & convenient" single SQL
statement syntax to follow with:

INSERT INTO EMAILLIST (EMAIL)
SELECT 'john(at)example(dot)net'
WHERE NOT EXISTS (SELECT 1 FROM EMAILLIST WHERE EMAIL =
'john(at)example(dot)net');

My question is, in a single threaded INSERT, this will *definitely* work.
Since ours is a web-based application, will this work out in a concurrent
multi-threaded environment too? In other words, will it be truly unique
when INSERT calls are concurrent?

Regards,
Gnanam