How many customers in the Northeast use Microsoft email?
the Northeast refers to Region = 'Northeast'; Microsoft email refers to email like '%@outlook.com'
SELECT COUNT(T1.email) FROM client AS T1 INNER JOIN district AS T2 ON T1.district_id = T2.district_id INNER JOIN state AS T3 ON T2.state_abbrev = T3.StateCode WHERE T3.Region = 'Northeast' AND T1.email LIKE '%@outlook.com'