cluster delivery doublemail

Since the cluster setup some e-mails are delived times * PMG members in cluster. MX Records show same prio or one has higher (therefore lower) prio and servs as backup. @ IN MX 10 pmg1.domain.de @ IN MX 10 pmg2.domain.de @ IN MX 30 pmg3.domain.de or @ IN MX 10 pmg1.domain.de @ IN MX 10...