When accessing webmail, the folder list is missing and the message list is not shown.
This is caused by when the server is upgraded to .Net 4.7. This version has a bug in a caching function where it is expired immediately.
For users running version 9, upgrading to version 9.75 or later will resolve the issue.
If you are running version 8 or earlier you can either uninstall the .Net 4.7 if this is not required by other software, or edit the following file in Notepad:
Between the <system.web> and </system.web> tags, add the following:
|Class:||PRB: Product Problem or Issue|
|Revised:||Tuesday, July 4, 2017|