Changing email and calendar systems in a large organization is not an easy project. There are many people. There are many moving pieces. There are many opinions. Also, it's difficult to make sure that everyone knows about the upcoming changes.
When the campus moved from Zimbra to Office 365 we had campus-wide informational meetings twice a month. We had ambassadors reach out to all departments. We sent email, had flyers, a pop-up booth (a couple times), and a front-and-center portal announcement hoping to reach every constituent.
Below you will see two HTML-formatted email and one portal announcement.