cosi non va:
select distinct email,settore,data,attiva from (select t1.email from email t1 join tabella2 t2 on t1.email=t2.email union select t1.email from email t1 join tabella3 t3 on t1.email=t3.email union select t1.email from email t1 join tabella4 t4 on t1.email=t4.email) T0 LIMIT 0, 25000

così non va:
select * distinct email (select t1.email from email t1 join tabella2 t2 on t1.email=t2.email union select t1.email from email t1 join tabella3 t3 on t1.email=t3.email union select t1.email from email t1 join tabella4 t4 on t1.email=t4.email) T0 LIMIT 0, 25000