Organization's administrators need Primary Mail Server Down notification in Status page and by mail.
Some customers have applications to look up calendars of others using primary server using user's document in Domino Directory. When the primary server goes down, such applications can no longer reach out calendars even other clustered serves are alive (*1). Even SC Notes mail service is in service at 99.9% for cluster environment, those applications have business impact much frequently because SC Notes each mail servers including the primary one have been down so frequently.
Currently no status alert is notified, thus administrators come to recognize primary mail server failure by user's complaint. If administrators notified to users immediately after the failure, users will be less frustrated.
*1 Programmed code has no way to find other clustered servers although Notes can do.