Here are the frequently asked questions for the email migration to Office 365 Mail.
From CUHK Webmail to Office 365 Mail
From Exchange to Office 365 Mail
Q: How to turn on the "cached exchange mode" in Outlook?
A: You may turn on the "cached exchange mode" before migrating mails from Exchange server to Office 365 Mail. The steps in detail can be found at Microsoft Support.
Using Office 365 Mail
Q: Why can't I update my “Email Drop Box” at https://cai.itsc.cuhk.edu.hk/alias/ after the email migration?