There was a MOTD/Alerts Zimlet that SFU built a few years ago. I found several references to it around but didn't find the actual code anywhere. Since this list is hosted through SFU, maybe they'll respond.
Matt
From: "Pablo E Garaitonandia" <peg11@psu.edu>
To: "zimbra-hied-admins" <zimbra-hied-admins@sfu.ca>
Sent: Tuesday, September 1, 2015 8:19:22 AM
Subject: MOTD RFE for Zimbra
Hey Folks,
I submitted a ticket for an RFE with zimbra. The request is for some type of Message of the Day (MOTD) for web UI users. I think this would be useful in that it will allow the administrators to get messages out to all of the end users for upgrade and outage announcements. Support pointed me out to an old RFE that already exists. I voted for it. If I could ask you guys to vote for it I would be grateful. Thank you.
https://bugzilla.zimbra.com/show_bug.cgi?id=34833
Regards,
Pablo Garaitonandia
Penn State University
ITS, Administrative Information Services
(814) 865-6385
pablo@psu.edu