From the document:
Starting with Lotus Notes Traveler 18.104.22.168, mobile devices running Apple iOS 5 have the ability to create, rename, move, and delete mail folders from their devices.
However, this feature is not enabled by default and must be enabled at the Lotus Notes Traveler server by the server administrator before these functions will succeed.
To enable folder management on Apple devices, set the configuration option AS_ALLOW_DS_FOLDER_CHANGES in the TrueSyncServer section of NTSConfig.xml to true, and restart Lotus Notes Traveler. Folder management on devices will then be available to Apple users. Note that folder operations on the device are only available when the device is online and is able to connect to the Lotus Notes Traveler server.