A NOT IN() la subconsulta se puede usar aquí, ya que MySQL no es compatible con MINUS .
SELECT
cand_email
FROM tbl_cand_data
WHERE can_email NOT IN (SELECT un_email FROM tbl_unsubscribe)
También se puede hacer con un LEFT JOIN , buscando valores NULL en un_email columna:
SELECT cand_email
FROM
tbl_cand_data
LEFT JOIN tbl_unsubscribe ON tbl_cand_data.can_email = tbl_unsubscribe.un_email
WHERE tbl_unsubscribe.un_email IS NULL
Para excluirlos de un grupo de UNION operaciones, envuelva el UNION grupo en () como subconsulta:
SELECT email FROM (
SELECT cand_email AS email FROM tbl_cand_data
UNION
SELECT emp_email AS email FROM tbl_emp_data
UNION
SELECT email FROM AS email tbl_uptade_list
UNION
SELECT feed_email AS email FROM tbl_feedback
UNION
SELECT admin_email AS email FROM tbl_admin_emails
) email_list
WHERE email NOT IN (SELECT un_email FROM tbl_unsubscribe)
