[nznog] Xtra(Yahoo) Mail going to 2nd MX by default

Hi All, Had a customer of ours, no one on xtra could send e-mails they just got bounce backs. In this instance the Secondary MX was not accepting mail (The Daemon had crashed), the primary was fine however and no one else had issues sending mail there. Does anyone know if this is some kind of feature with Xtra's mailservers, to choose the secondary over the primary MX? Regards, Joe.