SQL Query Optimization
This query avoids the Compute Scalar of your query and avoids any changes in your table structure.  Should perform well.  

SELECT dt.email
    , accept = CASE WHEN dm.[DOMAIN] IS NOT NULL THEN 'NO' ELSE 'Yes' END
FROM dbo.[Data] dt
    LEFT OUTER JOIN dbo.[DOMAINS] dm ON dt.email LIKE ('%@' + dm.DOMAIN)