It's been requested a few times
https://forums.plex.tv/topic/160805-do-more-with-announcements/?hl=announcements
https://forums.plex.tv/topic/155922-request-mini-one-way-message-board/?hl=messages#entry896528
https://forums.plex.tv/topic/155717-in-plex-messaging-or-messaging-to-email/?hl=messages#entry894606
https://forums.plex.tv/topic/152456-notepadnotices-feature-request/?hl=messages
https://forums.plex.tv/topic/143957-request-admin-message-to-users/?hl=messages#entry840422
https://forums.plex.tv/topic/125758-server-notification/?hl=messages#entry751342
https://forums.plex.tv/topic/117369-pms-messaging-system/?hl=messages#entry697546
