This simple query is driving me nuts.

I have a simple table:

customer_id
action_date
action

I want to get a distinct count of customer_id where the action = 'A'
and the MAX action date is between 01/01/2005 and 03/01/2005.

This seems simple, and here is my query:

SELECT MAX(action_date) action_date, count(distinct(customer_id))
FROM email_product_hist
WHERE action = 'A'
AND action_date BETWEEN TO_DATE('01012005','MMDDYYYY') AND
TO_DATE('03312005','MMDDYYYY')
AND customer_id NOT IN (SELECT customer_id FROM customer_account);

But people are telling me that this does not render the correct
results.......is there something I am missing??

Thanks!