DECLARE @Email VARCHAR(100) = 'nam.nguyen@ceezoo.com'

SELECT TOP 100 *
FROM dbo.Orders o
INNER JOIN dbo.Customers c ON c.ID = o.CustomerID
WHERE c.Email = @Email AND o.IsNotified = 0

UPDATE o
SET o.IsNotified = 1
FROM dbo.Orders o
INNER JOIN dbo.Customers c ON c.ID = o.CustomerID
WHERE c.Email != @Email AND o.IsNotified = 0