MailGate is being configured to use a new External Storage (either for the first time or changing the existing one). When you click on the "Test Connection to External Storage Device" button, it says "Connection failed!".

In the application log, there is the following error:
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INFO  [ExternalStorageConfigManager] attempt to use NFS4 failed, reverting to NFS
WARN  [Logger] Parameters: Invalid chunk ignored.
WARN  [Logger] Parameters: Invalid chunk ignored.
WARN  [Logger] Parameters: Invalid chunk ignored.
WARN  [Logger] Parameters: Invalid chunk ignored.
INFO  [ExternalStorageConfigManager] attempt to use NFS4 failed, reverting to NFS
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1. Check "Remote Directory:” entry under Admin UI > Administration > System Settings -> External Storage
2. Remove the "/" in front of the directory name, leave only the directory name itself.