Union Clause

Hi,

This is my query:

SELECT SUM(zcom) + SUM(ze) + SUM(zp)
FROM
    (SELECT count(DISTINCT(email)) FROM customers_lookup) zcom
    UNION
    (SELECT count(DISTINCT(email)) FROM customers_lookup) ze
    UNION
    (SELECT count(DISTINCT(email)) zp FROM customers_lookup) zp);


Basically I want to get a count from the three tables where the email
address appears in ALL THREE tables.  If an email does not exist in
all three tables, then I do not want it counted.......

I think I'm barking up the wrong tree with the query above......

John.